Leon, 35 Great Marlborough Street, London, W1

I ate lunch in Leon every day for about a year, back when I worked on the doorstep of a branch of this London mini-chain. I was lured in one day by the promise of healthy fast-food – as opposed to so many of its Soho neighbours, which offer either healthy food (no meat, no dairy, no fun) or fast-food (of which nothing need be said) – and soon I was scurrying back to work each day to eat slap-up "big dishes" of tangy Moroccan meatballs with brown rice and crunchy slaw, or sweet-potato falafel with punchy aioli straight out of the sticker-adorned brown-card box.

Once I'd exhausted the small but perfectly formed repertoire, I took to experimenting with the side dishes and sauces – adding grilled halloumi to my superfood salad and smothering grilled chicken with chilli sauce and hummus. I racked up so many loyalty stamps that I had free wheat-free chocolate brownies more often than was sensible. And I was happy.

Then I moved, and Leon became a memory. Until last week, when I had a "why do we eat out?" discussion with a friend. Why do we persist in trying new places all the time when what we should do is match the venue to the occasion, he wanted to know. He has a point, but it would be negligent for a reviewer to return to the same place again and again, not to say boring, but since I've never critiqued Leon, I think it's allowed. That and the fact that despite its reputation for turning out quick, tasty, healthy takeaways for breakfast and lunch, Leon has a little-known evening service, where you eat off a plate, rather than out of the brown boxes. There's even wine...

I take my children: Leon's plain-speaking, good-tasting food seems the right match for this occasion: an after-cinema supper that needs to be finished before bedtime. The Carnaby Street branch is bright and bold, with vintage books scattered about and an upholstered bench-seat stretching round the edge of the back-room. Up front are the tills, and in the middle, in full view, chefs whip up the dishes and send them either to the tables or down chutes to the waiting take-out customers.

The chitter-chatter of Soho's bright young things reverberates over a jazzed-up world-music soundtrack as we decide what to eat. Oddly, for the "we're a restaurant, really" service, ordering is via a printed pad: tick what you want and hand it to the waitress. My 11-year-old takes charge and wields the pencil, briskly ticking five "snacks" (hot chargrilled chorizo, grilled halloumi, warm Greek flatbread, hummus and marinated green olives). From a new kids' menu, she chooses meatballs. Teenboy has chilli con carne (having been dissuaded from a "meaty pan of pleasure" sharing platter), and I revert to my old favourite, grilled chicken. As I'm on parental duty I forgo a Leon Gin Mule, and we all have zingy Leon-made lemonades. I do make a mental note, though, to come back with grown-up friends for prosecco and those sharing plates.

One could quibble that the chefs are a little more heavy-handed on the brown rice than the meat, but that's all. The chicken's succulent, the meatballs are just the right side of spicy and Teenboy stows away the chilli in silent satisfaction. Having the snacky bits and little pots of sauces to add to the rice and meat makes this as much a posh picnic as a Brit version of a diner, and that's a good thing. It lends itself brilliantly to supper with friends (or family), where sticking forks into each other's food is indulged.

Those daytime brownies come gussied up with posh vanilla ice-cream at night, as does a hot lemon ginger crunch. Both are a sweet riposte to the deeply savoury dishes that have gone before, and a good espresso rounds things off.

The Leon ethos is one of local, seasonal, good-quality produce made into crowd-pleasing food at a realistic (if not cheap) price. The lengthy queues every lunchtime are testament to the chain's success – nine branches and counting. What's surprising is how well it works as an evening venue when the prices are pretty competitive – only £1 or so more than the take-out list. It deserves to be as well known as a restaurant as a take-away. It's nothing like the big fast-food chains, thank the lord – but if you want a posh pit-stop pre- or post-theatre/ cinema in London, Leon is just the place. n

14/20

Scores: 1-9 stay home and cook, 10-11 needs help, 12 ok, 13 pleasant enough, 14 good, 15 very good, 16 capable of greatness, 17 special, can't wait to go back, 18 highly honourable, 19 unique and memorable, 20 as good as it gets

Leon 35 Great Marlborough Street, London W1, tel: 020 7487 5280 Breakfast, lunch and dinner daily. £40 for dinner for two with wine

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Reviews extracted from 'Harden's London and UK Restaurant Guides 2010'. www.hardens.com