Wash the potatoes thoroughly and cut lengthways into thick pieces. Mix together the olive oil, chilli pepper, lemon zest, rosemary, pepper and salt. Thoroughly turn the potato pieces in the marinade. Preheat the oven to 200 degrees (gas level 4 - 5). Place the potatoes on a baking sheet and bake for about 25 minutes, turning every now and then. When the pieces are golden brown, they can be served.