Preheat the oven to 400°F (200°C) and place the oven rack in the top third position.
Place the 4 boneless, skinless chicken breasts side-by-side in a 9x13-inch baking dish.
Sprinkle the chicken evenly with 1/2 teaspoon garlic powder and season with salt and black pepper to taste.
Bake the chicken, uncovered, for 10 minutes.
While the chicken bakes, whisk together 1/4 cup honey, 1/4 cup Dijon mustard, 1/2 cup chicken broth, and 1 tablespoon cornstarch in a mixing bowl until smooth.
Remove the chicken from the oven and pour the honey–mustard sauce evenly over the breasts.
Return the dish to the oven and bake uncovered for an additional 15–20 minutes, or until the internal temperature reaches 165°F (74°C).
Remove the chicken, spoon sauce over the top again, and let rest for 5 minutes. Sprinkle with chopped parsley if using before serving.