Heat oven to 425°F. Line a large rimmed sheet pan with parchment for easy cleanup.
Toss potatoes with 1 tbsp oil and a pinch of salt and pepper. Spread on the pan and roast 10 minutes.
Slice sausage and prep remaining vegetables. In a bowl, combine sausage, peppers, zucchini, onion, and broccoli.
Drizzle with remaining oil. Add garlic, Italian seasoning, paprika, red pepper flakes, salt, and black pepper. Toss to coat.
Add sausage and veggies to the pan with potatoes. Roast 15–18 minutes, stirring once, until browned and tender.
Finish with lemon juice and parsley. Taste and adjust seasoning, then serve hot.