Prepare the Marinade: In a medium bowl, whisk together Dijon mustard, maple syrup, olive oil, minced garlic, apple cider vinegar, thyme, smoked paprika, salt, and pepper.
Marinate the Chicken: Place the chicken thighs in a large zip-lock bag or shallow dish. Pour the marinade over the chicken, ensuring it is well coated. Allow it to marinate for at least 30 minutes in the refrigerator (or up to 4 hours for more intense flavor).
Preheat the Oven: Preheat your oven to 400°F (200°C).
Sear the Chicken: In a large oven-safe skillet, heat a little olive oil over medium-high heat. Once hot, add the marinated chicken thighs (reserve the marinade) and sear for 3-4 minutes on each side until they develop a golden-brown crust.
Add Vegetables: Reduce heat to medium, then add the sliced red bell pepper, cherry tomatoes, and baby spinach to the skillet, distributing them around the chicken.
Bake: Pour the reserved marinade evenly over the chicken and vegetables in the skillet. Transfer the skillet to the preheated oven and bake for 20-25 minutes, or until the chicken is cooked through (internal temperature of 165°F / 74°C).
Serve: Carefully remove the skillet from the oven and let it rest for a few minutes before serving.
Notes
Serve straight from the skillet for a rustic feel, or plate the chicken and vegetables on a large platter, drizzling any remaining sauce over the top. Garnish with fresh thyme or parsley for added color.