Preheat your oven to 400°F.
In a large bowl, combine the olive oil, minced garlic, rosemary, salt, pepper, lemon zest, and lemon juice.
Add the chicken thighs to the bowl and toss to coat them evenly with the marinade. Let the chicken marinate for at least 30 minutes, or up to 2 hours in the refrigerator.
In a large oven-safe skillet, heat the chicken over medium-high heat, skin side down, for about 5-7 minutes until the skin is golden brown.
Flip the chicken and cook for an additional 3-4 minutes. Remove the chicken from the skillet and set aside.
In the same skillet, add the chicken broth and Dijon mustard, scraping up any browned bits from the bottom.
Return the chicken to the skillet, skin side up, and transfer the skillet to the preheated oven.
Bake for 25-30 minutes, or until the chicken reaches an internal temperature of 165°F.
Remove the skillet from the oven and let the chicken rest for 5 minutes before serving. Spoon some of the pan juices over the chicken for added flavor.