Halve the zucchini and cut into thin slices. Cut the leek into rings. Dice the onion and garlic.
Heat 2 tablespoons of oil in a pan and fry the chicken breast fillet all around until golden brown. Remove from the pan, season with salt and pepper and place in a baking dish. Add the rest of the oil to the pan and briefly sauté the onion and garlic. Add the zucchini and leek and stir-fry briefly. Season with salt and pepper and spread over the fillets.
Mix the cream with the mustard and season with sugar, salt, pepper and paprika. Pour the mustard cream evenly over the vegetables. Sprinkle with grated cheese and bake in the preheated oven at 175 ° for 20 minutes.