Prep the chicken: Pat chicken dry with paper towels.
If using breasts, pound to an even 1/2–3/4 inch thickness so they cook evenly. Season both sides with 1 teaspoon salt and black pepper.
Make the sauce: In a bowl, whisk together Dijon, whole-grain mustard, honey, Greek yogurt, apple cider vinegar, garlic, paprika, onion powder, and red pepper flakes. Taste and adjust sweetness or tang.
Add a pinch of salt if needed.
Preheat and heat the pan: Preheat oven to 400°F (200°C). Heat a large oven-safe skillet over medium-high. Add olive oil and swirl to coat.
Sear for flavor: Add chicken in a single layer.
Sear 2–3 minutes per side until lightly browned. Don’t cook through; just build color. Work in batches if needed.
Coat with sauce: Reduce heat to medium-low.
Pour the honey mustard sauce over and around the chicken, turning to coat. Spoon some sauce on top of each piece.
Bake to finish: Transfer skillet to the oven and bake 8–12 minutes, depending on thickness, until the internal temperature hits 165°F (74°C). The sauce should thicken and lightly caramelize around the edges.
Rest and garnish: Remove from oven and let rest 5 minutes.
Spoon pan sauce over the chicken. Finish with chopped parsley or chives.
Serve: Pair with steamed green beans, roasted broccoli, quinoa, brown rice, or a simple side salad. Spoon extra sauce over everything.