In a large heavy skillet, heat the oil over medium-high heat.
Sprinkle chicken with salt and pepper. Add the chicken and cook for 7-8 minutes, turning once or until the chicken is cooked through. Remove chicken from skillet and cover with foil on a separate plate, set aside.
Add onions to the skillet and sauté for 2-3 minutes until starting to soften. Add garlic and cook for one minute.
Add chicken stock, lime juice, cilantro, red peppers flakes, and salt and pepper to taste. Bring to a gentle boil for 8-10 minutes or until liquid is reduced by ¼ cup.
Stir in the sour cream during the last few minutes. Return chicken to the sauce.