Start by preheating your oven to 375°F. While it heats up, pat your chicken fillets dry with a paper towel and season both sides lightly with salt and pepper before setting them in your baking dish.
In a small bowl, whisk together the Dijon mustard, honey, chopped dill, orange zest, and olive oil until fully combined. If you're using garlic, stir it in now so the flavor has time to blend into the sauce.
Using a pastry brush, coat both sides of each chicken fillet generously with the honey mustard mixture. Make sure every piece is evenly covered so the flavor comes through in every bite.
Place the chicken in the preheated oven and bake for about 30 minutes, or until the internal temperature reaches 165°F. The top should look glossy and lightly caramelized from the honey.
Let the chicken rest for about 5 minutes once it comes out of the oven, which helps keep the juices locked in. Slice or serve whole alongside your favorite sides.