Preheat oven to 375.
In a large glass baking dish, add peppers, onions, garlic, olive oil, salt and pepper. Toss until all the vegetables are coated in the olive oil.
Place sausage links over vegetables and put in oven. Bake for about 20-25 minutes until vegetables are soft and sausages are cooked through.
Take sausage links out of baking dish and onto a cutting board. Slice sausage thickly on an angle, about 4-5 slices per link. Place sausage pieces back into baking dish.
Add a few ladles of tomato sauce into baking dishes and gently stir to combine with sausage and peppers.
Place sausage and peppers back into the oven for another 15 minutes or until sauce is bubbly.
Serve alongside pasta and/or bread and with Parmesan cheese.