Place clams and mussels in a large bowl, and cover with cold water. Sprinkle with cornmeal; let stand 30 minutes. Drain and rinse.
Coat a large Dutch oven with cooking spray; add oil, and place over medium heat until hot. Add the onion, bell pepper, and garlic, and sauté 5 minutes.
Add parsley and next 8 ingredients (parsley through tomato sauce); bring to a boil. Cover, reduce heat, and simmer 1 hour, stirring occasionally.
Add the clams, mussels, shrimp, and sea scallops, and stir well. Cover and cook over medium heat 8 minutes or until clam and mussel shells open and shrimp and sea scallops are done. Discard any unopened shells. Serve over pasta.