Heat 2 teaspoons olive oil in a saucepan over medium heat, and cook the onion and garlic until tender. Mix in crushed tomatoes, tomato paste, wine, sugar, salt, oregano, red pepper, and bay leaf. Simmer uncovered 1 hour, stirring occasionally.
Bring a large pot of lightly salted water to a boil. Place spaghetti in the pot, cook 8 to 10 minutes, until al dente, and drain.
Place the clams in a pot fitted with a steamer basket over boiling water, and steam until opened. Discard clams that do not open. Stir into the sauce.
Heat 2 teaspoons olive oil in a skillet over medium heat, and cook the shrimp and scallops 2 minutes, or until opaque. Mix in garlic. Stir into the sauce. Serve sauce with seafood over the cooked spaghetti, and top with Parmesan cheese.