Preheat the oven: Heat to 425°F (220°C).
Line a large rimmed sheet pan with parchment for easy cleanup, or lightly oil the pan.
Par-cook the potatoes: Since potatoes take longer, toss them with 1 tablespoon olive oil and a pinch of salt and pepper on the pan. Spread them out and roast for 10 minutes while you prep the rest.
Slice and prep: Cut the chicken sausage and vegetables. Aim for even sizes so everything roasts at the same pace.
Mix the seasoning: In a small bowl, combine salt, pepper, garlic powder, smoked paprika, oregano, and thyme.
Stir the Dijon into the remaining 2 tablespoons olive oil if using.
Toss everything together: Pull the pan from the oven. Add peppers, onion, zucchini, broccoli, and sausage to the potatoes. Drizzle with the seasoned oil and sprinkle the spice blend over the top.
Toss directly on the pan to coat well.
Roast until caramelized: Spread everything into an even layer with space between pieces. Roast 18–22 minutes, stirring once halfway, until veggies are tender and edges are browned.
Finish and taste: Remove from the oven and splash with balsamic vinegar or lemon juice. Toss, taste, and adjust salt and pepper as needed.
Garnish and serve: Sprinkle with chopped parsley.
Serve as is, or pair with rice, quinoa, or crusty bread.