Pre-heat the oven to 425°F.
Season the chicken with salt and pepper.
Toss the fresh fennel and onions with olive oil to dress lightly and arrange in a roasting pan or casserole dish.
Use a food processor to pulse-grind the fennel seed, garlic, herbs, chili pepper, lemon zest and onion flakes. Dress the chicken with seasoning and set on top of the fennel and onions. Roast for 45-50 minutes, then transfer everything to a warm platter.
Place the roasting pan on the stove over medium heat. Whisk up the pan juices with vermouth or wine, reduce by about half, whisk in the butter, then finish with lemon juice. Pour over the chicken, fennel and onions. Pass extra wedges of lemon and warm crusty bread for mopping.