Bring a large pot of lightly salted water to a boil. Place the beef in a very large, non-stick skillet and cook over medium heat, stirring frequently, until cooked through and crumbly. Drain away the excess fat, and then mix in the onion and bell pepper and cook 2 to 3 minutes more. While that occurs, cook the rotini in the boiling water until tender, about 8 minutes. When the onions and bell pepper have cooked 2 to 3 minutes, mix in the pasta sauce and water, bring to simmer, and simmer 5 minutes. When the pasta is cooked, reserve 1/2 cup of its cooking liquid and then drain the pasta well. Add the pasta and reserved cooking liquid, salt and pepper to the skillet and toss to combine. Serve, tableside, with freshly grated Parmesan cheese.
Note: If you don’t have a very large skillet, combine the meat sauce and rotini in heatproof bowl when asked to combine the two in the method. Serve immediately.