I would simply add some green peppers to the onions and garlic that go into almost every marinara in the world. Chop 'em small and saute with olive oil and garlic and onions and add tomatoes and seasonings. If you want no evidence of them -- use your blender or boat motor to stir it up.
Personally I loathe green peppers but hey -- one man's ceiling is another man's floor.
Cheers!
Shannon