Preheat oven to 400. In a large heavy skillet, heat 1 tablespoon of oil over medium high heat. Meanwhile, coat chicken legs with olive oil, salt, pepper, and oregano.
Place chicken legs in a single layer in the skillet. Cook for 4-5 minutes, flip. Add in onions, lemon juice and sliced lemons. Place skillet in the oven and continue to cook for 20-30 minutes or until the chicken reaches 165 degrees.