Peel, wash and quarter the potatoes. Cook in boiling salted water for about 20 minutes. Add peas to the potatoes about 5 minutes before the end of the cooking time. Wash cutlets and dab dry.
Cut a pocket into the schnitzel. Drain the tomatoes and cut into pieces. Mix with the pesto. Fill the schnitzel with the pesto and put it on a wooden skewer. Season schnitzel with salt and pepper.
Heat the oil in a pan. Fry the escalopes in it for about 4 minutes on each side. Peel onion and cut into thin rings. Add the onion rings to the schnitzel about 5 minutes before the end of the cooking time and fry until golden brown, turning.
Drain the potatoes and peas. Add milk and fat and mash coarsely to puree. Season to taste with salt and pepper. Arrange turkey escalope and puree on a plate, put onion rings on the escalope.