Preheat the oven to 200c/400f.
Wash and dry the chicken thighs, place the chicken thighs on a baking sheet lined with parchment paper and set aside.
In a small bowl combine the olive oil, zest of a lemon, smoked paprika, garlic powder, salt and pepper, mix well and coat the chicken thighs with this mixture on both sides. Bake the chicken thighs for 25 minutes on one side, then turn them around, lower the heat to 180c/360f and bake for an other 15 minutes. Remove from the oven and set aside.
While the chicken thighs are cooking prepare the honey garlic sauce.
Melt the butter in a medium sized skillet, sauté the onions until caramelized, add in the garlic and sauté for a couple minutes more, then add in the honey, tamari, the water, the lemon juice, bring to a boil stirring constantly. Add the lemon slices on top and let it simmer for a couple of minutes. When the sauce thickens turn of the heat.
Pour the honey garlic lemon sauce over the chicken thighs make sure they are fully coated, place the lemon slices over the chicken thighs and bake for another 10 minutes.
Let the honey garlic lemon chicken thighs cool for a while before handling them.