Preheat oven to 400°F.
If using raw sausage, cook sausages in a large skillet with a small amount of water, over medium heat. Continue adding water as it evaporates until browned and cooked through. Remove from heat and cut into ½ inch to ¾ inch slices. If using pre-cooked sausage, cut into ½ inch to ¾ inch slices first, then cook over medium heat to brown sausage. Remove from skillet and set aside. Add 1 Tbsp olive oil, garlic and onion to the pan, cook over medium heat until fragrant. Add dry orzo to pan and cook, stirring often to toast pasta, about 2 minutes.
Drizzle olive oil into a 9×13 inch oven safe baking dish. Add orzo, cooked sausage, garlic, onion, carrots, mushrooms, zucchini, red pepper, salt, pepper and parsley to baking dish. Stir to combine all ingredients. Pour in vegetable broth and stir again.
Bake 20 minutes, then remove baking dish from oven. Add the mascarpone cheese and sprinkle ½ cup of the parmesan over the top. Stir to combine all ingredients. Sprinkle remaining ½ cup of parmesan evenly over the top and bake for another 20 minutes until broth has evaporated and orzo is cooked through.