Place your chicken fillets in a tray in a pre-heated 180 C / Gas 4 oven for 15-20 mins.
Meanwhile prepare your sauce of the chopped tomatoes, chopped red chilli (de-seed if you dont like it too hot), garlic, chopped onion and salt and pepper. Simmer in the saucepan for about 10 mins, then remove your chicken from the oven and pour the sauce onto the chicken. Place back in the oven for a further 20-25 mins or until the chicken is completely cooked.
Remove from the oven once more and put the cheese over it and place it under a hot grill untill the cheese is melted and bubbling, delish!