Heat the oil over medium high heat in a heavy skillet. Add the chicken to the skillet (with some oil if needed) in a single layer. Season with salt and pepper. Cook for 4-6 minutes, flipping as needed until the chicken is just cooked through and lightly browned. Remove and set aside.
Add the garlic and cook for 1 minute until fragrant. Add the tomato sauce, and cumin. Cook for 3-5 minutes until tomatoes are softened and a thick, chunky sauce is forming. Season with salt and pepper if needed.