Preheat the oven to 400°F (200°C).
In a small bowl, whisk together Dijon mustard, whole grain mustard, olive oil, minced garlic, dried thyme, smoked paprika, salt, black pepper, and lemon juice until well combined.
Pat the chicken thighs dry with paper towels to ensure crispy skin.
Place the chicken thighs in a large bowl and pour the mustard mixture over them. Toss to coat each piece evenly.
Arrange the coated chicken thighs skin-side up on a baking sheet lined with parchment paper or a lightly greased baking dish.
Bake in the preheated oven for 35 minutes, or until the chicken reaches an internal temperature of 165°F (74°C) and the skin is golden and crispy.
Remove from the oven and let the chicken rest for 5 minutes before serving.