Preheat your oven to 425 degrees.
Spray a baking sheet with non-stick cooking spray and set aside.
In a large bowl, add sausage, potatoes, bell peppers, onion and fresh rosemary. Set aside.
In another bowl, add olive oil and Dijon mustard.
Whisk this together.
Then add minced garlic, grated Parmesan cheese, Italian seasoning, salt and black pepper.
Whisk together well.
Pour this over your sausage and veggies mixture.
Stir together until everything is evenly coated.
Place the mixture onto your prepared pan and spread out evenly.
Bake in the oven for 30 - 45 minutes or until the sausage is thoroughly cooked and the veggies are tender.