Prep the chicken: Pat the chicken breasts dry and pound thicker ends so each piece is an even 1/2–3/4 inch. This helps them cook evenly and stay juicy.
Make the sauce: In a bowl, whisk together Dijon, whole-grain mustard, honey, vinegar, olive oil, garlic, smoked paprika, onion powder, salt, and pepper until smooth.
Marinate: Add chicken to a zip-top bag or shallow dish and coat with half of the sauce. Reserve the other half for basting and serving.
Marinate 20–30 minutes at room temp or up to 8 hours in the fridge.
Choose your method: Bake: Heat oven to 400°F (200°C). Arrange chicken on a lined baking sheet. Bake 16–20 minutes, basting with some reserved sauce halfway, until internal temp reaches 165°F (74°C).
Pan-sear: Heat a large skillet over medium-high with a light drizzle of oil.
Sear chicken 4–5 minutes per side. Lower heat to medium, brush with sauce, and cook 1–2 more minutes until done.
Rest and glaze: Transfer chicken to a plate and rest 5 minutes. Spoon over a little more sauce for a glossy finish.
Garnish and serve: Sprinkle with chopped herbs and a squeeze of lemon if you like.
Pair with rice, quinoa, roasted broccoli, or a simple green salad.