Preheat the oven to 200°C.
Cut the potatoes & onion onto 1 cm rings. Roughly chop 2 garlic cloves.
Lightly oil a deep casserole dish and layer the base with the potato and onion slices. Scatter the chopped garlic over them , then drizzle with olive oil and season with salt and pepper. Place the chicken on top. Put the garlic in the cavity, then scatter half of the oregano over the chicken, season with salt and pepper, drizzle with oil, then put in the oven for 15-20 minutes until the chicken skin is golden and crispy.
Meanwhile dice the aubergine and red pepper.
Take the dish out of the oven and scatter the olives, aubergine and pepper pieces around the chicken then scatter the remaining oregano over them. Pour the chopped tomatoes evenly over the veggies then season with salt and pepper.
Turn the oven down to 170°C. Put a lid on the dish then gently bake the chicken for 60-90 minutes, depending on its weight.
Check the chicken legs – if clear liquid is coming out when poked, the chicken is cooked through.
Rest the chicken for 5 minutes while you adjust the seasoning of the sauce to your liking.
Carve the chicken and serve with the veggies and tomato sauce.