1. Heat a large nonstick skillet over medium heat. Add 1 teaspoon oil to pan, and swirl to coat. Add 1/2 cup chopped onion and garlic; cook for 2 minutes, stirring frequently. Place mixture in food processor. Add oats and next 8 ingredients (through egg); process until smooth.
2. Wipe pan with a paper towel. Return pan to medium heat. Add remaining 2 teaspoons olive oil to pan, and swirl to coat. Working with one portion at a time, spoon bean mixture into a 1/2-cup dry measuring cup, and carefully remove bean mixture with a rubber spatula onto pan. (Bean mixture is very soft and sticky.) Using spatula, shape mixture into a 3/4-inch-thick round patty. Repeat procedure 5 times to form 6 patties. Cook 8 minutes or until golden, turning after 4 minutes.
3. Combine sour cream, 2 tablespoons grated onion, and cheese in a small bowl. Spread about 2 tablespoons sour cream mixture into each pita half; top with 1 lettuce leaf, 1 tomato slice, and 1 bean patty.