Preheat the oven: Heat to 425°F (220°C).
Line a large sheet pan with parchment for easy cleanup, or lightly oil it.
Prep the veggies: Cut everything into similar, bite-size pieces so they roast evenly. Keep broccoli florets small and onions in wedges so they caramelize without burning.
Combine on the pan: Add sausage, bell pepper, red onion, broccoli, zucchini, and cherry tomatoes to the sheet pan.
Season well: Drizzle with olive oil. Sprinkle salt, pepper, garlic powder, smoked paprika, oregano, and red pepper flakes over everything.
Toss right on the pan until all pieces are coated and spread in an even layer.
Roast: Bake for 15 minutes, then stir and spread back out. Roast 8–12 more minutes, until veggies are tender with browned edges and sausage is sizzling.
Add brightness: Right out of the oven, drizzle with balsamic vinegar or a squeeze of lemon. Toss gently.
Finish and serve: Taste and adjust salt and pepper.
Sprinkle with parsley. Serve as-is, or with rice, quinoa, couscous, or crusty bread.