In a 12-inch non-stick skillet, heat the olive oil over medium-high heat until you begin to smell the oil. Add the chicken sausage and cook, breaking the meat apart with a spoon or spatula until it's browned. Stir in the garlic, fennel seed, italian seasoning and crushed red pepper flakes.
Stir in the tomatoes, water, 1/2 tsp sea salt, then add the pasta. Raise the heat some and stirring often, cook at a vigorous simmer until the pasta is tender and the sauce has thickened, about 15-18 minutes.
Taking a handful at a time, stir in the chopped spinach and cook until it has wilted. Top with the mozzarella cheese and serve.