In a bowl, combine lemon zest, lemon juice, honey, olive oil, salt, black pepper, red chili flakes, paprika, garlic powder, and mustard powder.
Coat the chicken thighs thoroughly with the prepared marinade.
If using the oven, heat it to 400°F (200°C).
Place the coated chicken on a lined baking sheet and arrange lemon slices around and on top.
Cook for 35-40 minutes until the chicken reaches 165°F (75°C) and the skin turns golden and crisp.
For extra crispiness, broil on high for the final 2 minutes.
Remove and let the chicken rest before serving.
If using an air fryer, preheat it to 375°F (190°C).
Arrange chicken in a single layer in the basket with lemon slices.
Cook for 18-22 minutes, flipping halfway, until the internal temperature hits 165°F (75°C) and skin is crispy.
Broil on high for the last 2 minutes for a crunchy finish.
Let chicken rest briefly before serving.