Heat your oven to 180°C/Fan 160°C/Gas 4. Finely grate the zest from the lime. Juice it. Peel and crush 1 garlic clove. Put the lime zest, juice and garlic into a dish and stir in 2 tsp sumach and a pinch of salt.
Put the chicken breasts between 2 sheets of cling film or greaseproof paper. Bash them with a rolling pin till they're around 2cm thick. Add them to the dish and turn a few times to coat them in the sumach marinade. Set aside to marinate for 5 mins.
Line a baking tray with foil. Put a frying pan on a high heat for 2 mins to warm up. Add ½ tbsp olive oil to the pan. Lay the chicken steaks in the pan. Fry for 3-4 mins till golden brown underneath. Flip the chicken steaks over. Cook for another 3 mins till the chicken is browned all over.
Lift the chicken steaks out of the pan and lay them on the baking tray. Roast for 15-20 mins till they're cooked all the way through – when you insert a knife the juices should be clear and the flesh white all the way through.
While the chicken roasts, tip the buckwheat into a small pan. Pour in enough boiling water to cover the buckwheat by 1cm. Cover, bring to the boil, then turn the heat down and simmer for 15-20 mins till tender.
While the chicken cooks, finely shred the lettuce leaves and tip them into a large bowl. Dice the tomatoes and add them to the lettuce. Pick the leaves off the mint and basil sprigs. Tear them into small pieces and add most of them to the bowl.
Juice half the lemon. Peel and grate or crush the remaining garlic clove. Whisk the lemon juice and garlic with 2 tsp olive oil and a pinch of salt and pepper. Taste and add more salt and pepper if you think it needs it. Add the dressing to the salad bowl and toss to mix.
Serve the chicken steaks with the dressed chopped salad and buckwheat. Sprinkle over the remaining herbs.