Pre-heat the oven to 200°C/400F and line or grease a baking tray.
If your chicken breasts are quite thick, put the chicken breasts on a chopping board, cover with clingfilm or baking paper and using a rolling pin or the bottom of a saucepan, flatten them out (this is optional).
Place the breasts on to the baking tray.
Mix the passata with the garlic powder and oregano and divide between the chicken breasts, spreading out to cover. (If you have any left, you can pour it into the dish around the outside of the chicken.)
Top the chicken breasts with the slices of pepper and mushroom and then sprinkle over the cheese. Pop into the oven.
Bake for 18-20 minutes until the chicken is cooked through and the cheese golden.
Serve with the optional basil.
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