Preheat the oven to 425°F (220°C).
Arrange the halal Italian-style sausage links, sliced bell peppers, and onions on a large sheet pan.
Drizzle with olive oil.
Sprinkle evenly with Italian seasoning, garlic powder, red pepper flakes, salt, and black pepper.
Toss the vegetables until evenly coated while keeping the sausages directly against the baking sheet.
Bake the Sheet Pan Sausage and Peppers for 20 minutes.
Turn the sausages over and continue baking for 10–15 minutes until browned and the internal temperature reaches 160°F (71°C).
Remove from the oven and let everything rest for 5 minutes.
Garnish with fresh basil if desired.
Serve warm with marinara sauce, crusty bread, pasta, rice, or mashed potatoes.