Cut sausage into 1-inch chunks (cutting is easiest when sausage is partially frozen).
Coat a large baking sheet with nonstick cooking spray. Combine raw sausage pieces, potatoes, bell peppers, onion and garlic on baking sheet. Drizzle with olive oil. Sprinkle with Italian seasoning, salt, pepper, and crushed red pepper flakes, if desired. Toss to coat evenly. Spread ingredients out in a single layer.
Bake for 40-45 minutes, or until sausage is fully cooked and vegetables (incl. potatoes) are tender.