Preheat the oven to 425°F. Line a large sheet pan with parchment paper for easy cleanup.
Place the halved potatoes on the sheet pan. Drizzle with 1 tablespoon olive oil, then sprinkle with salt, black pepper, and garlic powder. Toss to coat evenly and spread into a single layer.
Add the sliced bell peppers and onion to the same pan. Drizzle with the remaining tablespoon of olive oil and toss lightly with the potatoes.
Nestle the Italian sausages among the vegetables and potatoes. Sprinkle Italian seasoning over everything.
Roast for 25 to 30 minutes, flipping the sausages and stirring the vegetables halfway through. Cook until the potatoes are golden and crisp on the edges and the sausages reach an internal temperature of 160°F.