Using a round steel cutter, cut a cylinder of meat out of the middle of the fillets.
Brown the fillets in a frying pan in a little oil over a moderate heat. When the fillet is still rare, add the garlic, guanciale, sage, half the mushrooms, the parsley and cook through.
Separately, toss the remaining mushrooms with a little oil, adding the strips of tomato and chilli pepper.
At the same time, cook the cylinders from the fillets in a frying pan over a high heat for a few minutes. Season to taste with salt and pepper.