Put a large pan of salted water on to boil. Scrub the new potatoes and chop them into bite-size chunks. Set aside.
Set a frying pan over a medium heat. Add the walnut halves and toast for 2-3 mins till they're browned and smell nutty. Tip onto a board, let them cool for a few mins then roughly chop them. Pop them in a bowl.
Finely grate the zest of the lemon into the bowl. Squeeze in the juice. Halve the chilli, scoop out the seeds and white pith and finely chop it. Add to the bowl. Finely chop the mint leaves and add them too. Stir to mix and set aside.
The water should be boiling by now, so add the potatoes. Pop a lid on the pan and simmer the potatoes for 15 mins till they're tender when pressed with a fork.
While the potatoes simmer, peel and crush or grate the garlic clove. Stir into ½ tbsp olive oil with a pinch of salt and pepper. Place the chicken breasts between 2 sheets of baking paper. Bash with a rolling pin or a pestle till they're around 2cm thick. Rub in the garlic and oil.
Put the frying pan back on a medium heat. Warm it up for 2 mins, then add the chicken breasts. Fry for 5 mins till browned, then flip and fry for another 5 mins. The chicken should be cooked through – if you slice into it, there should be no pink.
While the chicken cooks, toss the lettuce leaves with ½ tbsp olive oil and some salt and pepper.
The potatoes should be cooked by now, so drain them well. Pop the chicken breasts onto 2 warm plates and heap up the potatoes and salad next to them. Spoon over the crushed walnut, lemon and mint salsa and serve.