Heat the oven to 200C (180C fan)/390F/gas mark 6.
To make the meatballs, put the chicken breasts (or mince) in a food processor and add all the remaining meatball ingredients and a pinch each of salt and pepper.
Blitz smooth, then roll into 16 meatballs.
Swirl a few tablespoons of the passata around the base of a 24 cm x 32 cm roasting tin.
Mix the remaining passata with the Turkish pepper flakes, dried oregano, garlic powder and a big pinch of salt and pepper.
Arrange the meatballs in the roasting tin, then pour the sauce over the top to cover.
Bake for 12-15 minutes, until the meatballs are cooked through - cut one in half to test: it should be pale in colour and firm-textured all the way through.
If it's not quite there, return the tin to the oven for a few minutes more, until the meatballs are cooked.
Crumble the remaining 50 g feta over the top, scatter on the parsley and serve immediately.
