Peel and finely dice the onions. Heat oil in a pot and fry 1/3 of the onions in it. Add spinach, defrost at low heat and cook for about 16 minutes. Season with salt and pepper. Soak the rolls. Put minced meat and ground pork in a bowl. Add remaining onions, eggs and squeezed out roll and knead. Season with mustard, salt, pepper, thyme and paprika powder.
Drain the peppers on a sieve and cut them into strips. Fold the pepper strips, except for a few for garnishing, under the spinach. Drain the Mozzarrella and cut into slices. Grease a large casserole dish. Spread half of the minced meat in the dish. Spread the spinach on top.
Spread the mozzarella, except for 5 slices, on the spinach. Sprinkle half of the Gouda on top. Spread the rest of the minced meat on top. Roast in the preheated oven (electric cooker: 200 °C / convection oven: 175 °C / gas: level 3) for about 1 hour. After half the roasting time, spread the remaining strips of pepper, mozzarella slices and Gouda cheese on top. Serve garnished with thyme.