Make the marinade: Grind the fennel and coriander seeds. Mix sugar, salt, and orange zest in a bowl until fragrant. Add spices, sage, tarragon, mustard, and olive oil; mix until combined.
Prep the chicken: Pat dry the chicken, cut around the spine, and flatten the breast. Spread the marinade over the chicken and let it marinate.
Prep the pan: Preheat the oven to 425°F (220°C). Slice the oranges, fennel, and shallots. Add olive oil to a pan, layer with oranges, fennel, shallots, and orange juice. Place the chicken on top.
Bake: Cover with foil and bake for 20 minutes. Remove foil and bake for an additional 30 to 40 minutes, basting occasionally.
Carve and serve: Remove the chicken, carve, and plate with remaining vegetables and pan juices. Optionally, make stock with scraps.
