In a large saucepan or Dutch oven, heat the oil over medium-high heat. Add the onion and cook until translucent, about 5 minutes. Add the garlic and red pepper (optional)—cook for 30 seconds. Add chicken, salt, cumin, oregano, and chili powder. Cook, stirring frequently until the chicken is cooked through, about 5 minutes. Stir the flour into the chicken mixture.