Place the chicken breasts in a large shallow bowl, pour over the buttermilk and leave to marinate for 2 hours or overnight if time allows
Preheat the grill to medium-high. In a large shallow bowl, mix together the breadcrumbs, lemon zest, chilli flakes, half the oregano and the Parmesan and season with salt and pepper.
Remove the chicken from the buttermilk, shake off the excess and then coat in the crumbs. Spray the chicken with 1-cal cooking spray
Place the chicken on a baking tray and grill for 15 minutes, turning half way through, until golden on both sides and cooked through
Meanwhile, preheat the oven to 220˚C/425˚F/Gas mark 7. Place the courgettes in a shallow ovenproof dish, drizzle with balsamic vinegar and scatter with the rest of the oregano. Season with salt and pepper and spray with 1-cal cooking spray. Bake for 10 minutes, then place the cherry tomatoes on top and bake for 8–10 minutes, until the courgettes are just tender and the tomatoes have softened
Serve a piece of chicken per person and then divide the tomatoes and courgettes between the plates.