Heat oil in a large skillet over medium heat. Add onion; cook and stir until softened, 3 to 4 minutes. Add bacon; cook for 1 minute. Stir in diced tomatoes, tomato sauce, water, and green beans; bring to a simmer. Add cavatappi; cook, stirring frequently, until tender, 8 to 9 minutes.
Sprinkle mozzarella cheese over the cavatappi mixture. Cover and cook until cheese is melted, 2 to 3 minutes. Season with salt and pepper.