Preheat the oven to 400F and put the baking rack in the middle position.
In a medium-sized bowl, add the sliced bell peppers, sliced onions, olive oil, garlic salt, pepper, Italian seasoning, and balsamic vinegar and combine.
Lay the sausage on the baking sheet, add place the pepper onion mix around it.
Bake the sausage and peppers for 10 minutes, flip the sausage and stir the pepper onion mix.
Continue cooking until the sausages are browned and the peppers are cooked through, which took about 25 minutes. The internal temperature of the sausage should be at least 165F. Enjoy!
Notes
We used aged balsamic vinegar from Trader Joes which is a little thicker than regular, but regular works totally fine too.If you're wanting to make plain baked Italian sausages without the peppers, they only take about 15 minutes to bake. Adding peppers or vegetables to the pan increases the cooking time.Either uncooked sweet Italian sausage, mild, or spicy sausage, or uncooked chicken Italian works for this recipe. Use the packaged variety like Johnsonville or another similar brand, the sausages from the meat counter are larger and would take longer to cook.We used about 1 lb of quick-cooking veggies, feel free to swap for others that cook fast.