Preheat the oven to 400 degrees. Combine the garlic powder, smoked paprika, Italian season, salt and pepper in a small bowl, then add the olive oil and stir until incorporated.

Place the sweet potato, bell peppers and red onion on a large rimmed baking sheet. Drizzle the olive oil spice mixture over the vegetables and toss well to coat. Arrange the vegetables in a single layer.

Nestle the Italian sausages into the vegetables, then place in the oven. Roast for 20-30 minutes until the internal temperature of the sausage is 160 degrees, turning halfway during the cooking time for even browning. If the sausages are done before the vegetables, simply remove them from the pan, place on a plate and cover them with foil, then continue cooking the vegetables until they're done.

Remove the pan from heat and serve hot with grainy mustard as desired. Enjoy!