Prepare the Peach Glaze: In a medium bowl, combine peach preserves, olive oil, soy sauce, vinegar, mustard, garlic, salt, black pepper, and red pepper flakes.
Season the Chicken: Pat the chicken dry. Mix salt, black pepper, and chili powder in a small bowl. Rub this mixture all over the chicken thighs.
Cook the Chicken: Heat olive oil in a large nonstick skillet over medium heat. Add chicken thighs and cook for 5 minutes on one side. Flip the chicken, reduce heat to medium-low, and cook for another 5 minutes, or until it reaches an internal temperature of 165°F.
Sauté the Peppers and Peaches: Increase heat to medium, add jalapeno slices to the skillet, and cook for 3 minutes. Add sliced peaches and continue to cook for 3 more minutes until peaches soften.
Combine and Finish: Pour the peach glaze over the jalapenos and peaches in the skillet. Stir well to coat. Return the chicken to the skillet, spooning the glaze over the chicken. Cook for an additional 1-2 minutes until the chicken is thoroughly heated.