In a large skillet, cook the onion, parsley and garlic in the olive oil for 5 minutes. Add the ground beef and cook until the meat is cooked through. Add the zucchini and mix well. Stir in the pesto or basil, tomato sauce, salt and pepper and red pepper flakes. Cook over low heat for 20 minutes, stir frequently. Cook pasta according to package instructions for al dente. Stir the heavy cream into the pasta sauce and heat through, taste for seasoning and adjust to your taste. Drain pasta and toss with sauce. Top with grated cheese.