Heat 2 tablespoons oil in 12-inch nonstick skillet over medium heat. Layer half of potato, onion and bell pepper slices in skillet. Season with salt and pepper. Repeat layering and seasoning. Cover and cook until potatoes and vegetables are tender, stirring and turning frequently with spatula, about 20 minutes. Sprinkle thyme over. Cool slightly.

Whisk eggs in large bowl to blend. Season with salt and pepper. Add potato mixture to eggs. Wipe skillet clean. Heat 1 tablespoon oil in same skillet over medium-low heat. Pour egg mixture into skillet; sprinkle with cheese. Cover and cook until eggs are just set, about 10 minutes. Slide frittata onto platter. Sprinkle parsley and capers over. Cut into wedges and serve.