Preheat your oven to 400°F. Line a large baking sheet with parchment paper.
In a large bowl, combine the olive oil, Italian seasoning, garlic powder, salt, and pepper. Toss the sausage, potatoes, bell peppers, and onions in the seasoning mix until evenly coated.
Spread the seasoned sausage and vegetables in a single layer on the prepared baking sheet. Be sure not to overcrowd the pan to ensure everything roasts evenly.
Roast the mixture in the preheated oven for 25-30 minutes, stirring halfway through the cooking time, until the potatoes are tender and golden brown and the sausage is browned.