In a bowl, whisk together the maple syrup, dijon mustard, olive oil, lemon, salt, and pepper. Add to a large bowl or bag with the chicken and submerge the chicken in the liquid, coating all of it in the maple mustard mixture.
Let marinate for at least 20 minutes, then preheat the oven to 400 degrees Fahrenheit.
Heat a large cast iron or other oven safe skillet over medium high heat. Once heated, place the chicken thighs skin side down in the skillet. Sear for 3-5 minutes or until golden brown. Flip and sear the other side for about 3 minutes.
Pour the remaining maple mustard marinade over the chicken in the skillet. Transfer to the oven and bake for 25-35 minutes or until the chicken is cooked through to an internal temperature of 165 degrees Fahrenheit and the skin on the top is nicely browned.