Partially cook bacon 3 minutes in a nonstick skillet; drain and set aside.
Position knife blade in food processor bowl; add quartered onion. Process until finely chopped. Add cheese and next 3 ingredients; process until onion is minced, scraping sides of processor bowl occasionally. Set aside.
Place toasted bread slices on a baking sheet; spread cheese mixture evenly over slices, spreading to edges of bread. Cut each small tomato into 4 slices. Top each slice of bread with a tomato slice and 2 bacon pieces. Broil 5 1/2 inches from heat (with electric oven door partially opened) 2 to 2 1/2 minutes or until cheese melts and bacon is crisp. Sprinkle with green onions. If desired, garnish with cherry tomatoes and fresh oregano.