Cook macaroni in boiling salted water for 8-9 minutes. Add peas for the last two minutes. Clean, wash and chop the tomatoes. Cut bacon into small cubes. Drain the pasta and let it drain.
Whisk milk and eggs, season with salt, pepper and nutmeg. Grease a round casserole dish (26 cm Ø; 1.5 litre capacity). Layer macaroni, bacon and vegetables in a circle. Pour the egg milk evenly over it.
Sprinkle everything with cheese. Bake in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for 35-40 minutes. In the meantime, peel and finely dice the onion. Wash the oregano, dab dry, put aside a little for garnishing, chop the rest finely.
Heat the oil in a pot. Fry the onion and oregano in it. Add the strained tomatoes and stock. Let simmer at low heat for about 10 minutes. Season to taste with salt, pepper and sugar. Serve the sauce with the macaroni tart.
Garnish with oregano set aside.