Lightly oil a baking tray. Peel onions and garlic. Chop garlic and 1 onion finely. Cut the rest of the onion into thin slices. Peel the sweet potatoes, quarter them lengthwise and cut into pieces.
Wash the rosemary, dab dry, pluck the needles and chop. Mix the onions, potatoes, 2 tablespoons of oil and half of the rosemary. Season with salt and pepper. Place on one half of a baking tray.
Preheat oven (electric cooker: 200°C/circulating air: 175°C/gas: level 3). Knead minced meat, ground pork, egg, breadcrumbs, garlic and onion cubes, milk and mustard. Season with salt and pepper. Form 8-12 small meatballs from the mixture and place on the other half of the baking tray.
Bake in the oven for 40-45 minutes.
Meanwhile clean and wash the peppers and courgettes and cut them into thick strips or slices. Mix with 1 tablespoon of oil, salt, pepper and the rest rosemary. After about 20 minutes of frying time, place on the tray.
Turn the meatballs once, turning the vegetables from time to time. Season with salt and pepper. Arrange everything.