Dice the tomato, onion, cooked potato, and olives. Drain the cans of tuna. In a skillet, heat a little oil and sauté the onion. Add the tomato, then the tomato puree, a splash of water, salt, pepper, garlic powder, parsley, and the tuna. Cook for 3 minutes, then add the olives. Stuff the peppers with this mixture.

In another skillet, prepare a sauce by adding the tomato puree and seasoning with salt, pepper, and parsley. Add a little water to thin it out. To serve, pour a layer of the sauce on the plate and place the stuffed pepper on top.