Clean, wash and cut the tomatoes into pieces. Rinse chicken filet cold, dab dry and cut in half. Put 1-2 sage leaves on each. Fry in hot oil for about 15 minutes. Turn several times, season with salt and pepper. Remove meat from the pan and keep warm.
Peel and chop the onions and fry them in the frying fat until transparent. Add tomatoes and braise for about 45 minutes while stirring. Add pepperoni. Season with tomato seasoning salt. Arrange chicken fillets on top