Meanwhile, in a non-stick skillet, heat oil over medium heat. Add garlic, green peppers, red onions and oregano and cook for 7 minutes or until softened, stirring occasionally. Stir in tomatoes, black olives and green onions and cook 1 minute more. Remove from heat. When potatoes are cool enough to handle, cut in half lengthwise and scoop out flesh, leaving shells intact.
Place shells on baking sheet.
Mash potato and add yogurt, milk and 1oz feta. Stir in vegetable mixture. Divide amoung potato skin shells, sprinkle with remaining feta and bake for 15 minutes or until heated through.