Peel onion and garlic and cut into fine cubes. Knead meat, onion and garlic, mustard, egg, breadcrumbs and milk. Season with salt and pepper. Form minced meat into meatballs and put them on an oiled baking tray.
Cook in the preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: level 3) for approx. 40 minutes. In the meantime, peel the potatoes, quarter them lengthwise and cut into slices. Clean, wash and cut the peppers into thick strips.
Wash, clean and slice the zucchini. Peel shallots and cut them into slices. Season vegetables with salt and pepper. After about 20 minutes spread them on the meatball tray and drizzle with oil.
Wash the rosemary and shake dry. Pluck the needles from the twigs and chop them finely, except for a little garnish. Sprinkle rosemary over the vegetables about 5 minutes before the end of the baking time. Decorate with rosemary before serving.