Preheat oven to 400°F and line a large sheet pan with parchment paper.
Arrange the sausage links on the prepared pan and bake for 10 minutes.
While sausages are baking, toss the sliced peppers and onions with olive oil, garlic powder, Italian seasoning, salt, and pepper in a large bowl.
Remove the pan from the oven, add the seasoned vegetables around the sausages, and return to oven.
Bake for an additional 20 minutes, stirring vegetables once halfway through, until sausages reach an internal temperature of 160°F and vegetables are tender and caramelized.
Let rest for 5 minutes before serving.