Preheat the oven to 375 degrees . In a large bowl, toss the sausage, potatoes, mushrooms, onion, garlic and olive oil; season with salt and pepper. Transfer to a baking sheet and cook, tossing occasionally, for 30 minutes.
Add the tomatoes to the sausage and vegetables and stir to coat. Arrange the mixture in an even layer and continue cooking for 30 minutes. Top with the parsley.