Preheat oven to 425°F. Grease a large baking sheet with spray oil.
Place the peppers and onions on the baking sheet. Toss with olive oil, salt, pepper, Italian seasoning, garlic powder, and red pepper flakes (if using). Stir well to coat and arrange vegetables in an even layer.
Nestle the sausages in between the vegetables.
Bake for 20 minutes, flip the sausages and stir the vegetables. Bake for another 15-20 minutes or until sausages are cooked through and vegetables are very tender.
If desired, place under the broiler positioned at least 2-3 inches away from the broiler for a slight char.
Garnish with freshly chopped basil or parsley. Serve and enjoy!
Notes
Make ahead: peppers and onions can be sliced ahead of time and stored in the refrigerator until ready to use. Cooked sausage and pepper leftovers also reheat well. Storage: Store leftovers in an airtight container in the refrigerator for up to 3 days. Reheat gently in the oven or microwave. To freeze: You can freeze this meal by separating the sausages from the vegetables. Then store each in airtight containers or freezer bags for up to 3 months. The vegetables will change in texture and can become a little soggy when thawed but will still be delicious.To thaw: Place this meal in the refrigerator overnight to thaw. Reheat in the oven or microwave until heated through. Spread the peppers and sausages out in an even layer to allow for even cooking. I recommend slicing the onions slightly wider than the peppers because the peppers take a little longer to cook than the onions. Place under the broiler for 2-3 minutes for a slight char if desired.