In a large pot, add rotini, mushrooms, diced onion and basil, optional red pepper flakes, salt, 3 cups of cold water and 1 cup of marinara sauce

Place pot on burner and turn to high

Cook 10-12 minutes, stirring frequently, until pasta absorbs most of the liquid and has cooked through. Be careful not to burn the bottom (avoid this by stirring often and removing from heat after most of the water absorbs)

After pasta has cooked, remove from heat and stir in remaining marinara sauce and cheese. You could also stir in half of the cheese and keep the remaining amount out for topping.