Preheat the oven to 400 degrees.
In a mixing bowl, whisk together the oil, orange juice, mustard, salt and pepper to taste.
Heat a large cast skillet over med-high heat. Add 1 Tbsp oil and chicken thighs skin side down. Season with sea salt and black pepper.
Brown the chicken skin for about 2-3 minutes, then turn it on the other side.
Add the orange slices, thyme sprigs, onion and fennel wedges, and the fennel seeds into the pan.
Pour the orange sauce over the top of the chicken and roast in the preheated oven for about 45 minutes, until chicken is tender and fully cooked.