Cut the eggplants into slices and leave them in salted water for a bit. 

Wash them, dry and place them in a baking tray. Brush them with olive oil and grill on both sides. 

Meanwhile, prepare the sauce. Sauté the onion and garlic, add the pepper and after a while the tomatoes and the tomato paste, continue with salt and pepper and leave the sauce to simmer and absorb all its liquids. 

Place a layer of eggplants in a baking tray, 3-4 spoonfuls of sauce over them and then a layer of cheese and feta.

Repeat the process until you run out of ingredients. 

Bake in the oven for 30 minutes. 

Serve hot.