Use a deep oven safe skillet, sauté onions and garlic in olive oil. Transfer to a small bowl. Save the skillet for later use.
Whisk eggs in large bowl, add tomatoes, herbs, sautéed onions and garlic.
Add olive oil to coat bottom and sides of original skillet. Pour in egg mixture and cook on medium-high until eggs are nearly set. While eggs are cooking, turn on your oven’s broiler.
Arrange peppers on top of frittata and sprinkle on feta cheese.
Place skillet 4-6 inches under broiler, until the top is golden brown.
Garnish with fresh oregano.