2. Preheat oven to 400. Slice and coat onion in a bit of olive oil. Spray baking sheet with non-stick cooking spray. Scatter onion slices on baking sheet. Arrange chicken on top of onion. Roast until chicken is cooked through or until golden brown, about 20 minutes. Remove tray from oven and let cool for a few minutes. Sprinkle chicken and onion with cilantro and serve warm.