Preheat your oven to 425°F (220°C).
Slice the turkey sausage and chop all the vegetables into bite-sized pieces.
Arrange the sausage, bell peppers, broccoli, and red onion on a large sheet pan.
Drizzle with oil.
Add the Dijon mustard, dried herbs, garlic powder, salt, black pepper, and crushed red pepper flakes.
Toss everything until the vegetables and sausage are evenly coated.
Spread everything into a single layer for even roasting.
Bake for 20 minutes, or until the vegetables are tender and lightly caramelized.
Serve your Sheet Pan Sausage and Veggies immediately with rice, mashed potatoes, crusty bread, or enjoy it on its own.