Preheat your oven to 400° degrees. Season the halibut fillets with salt and cayenne pepper, then drizzle with olive oil. Place the fillets on a baking sheet and bake for 12-15 minutes or until the fish flakes easily with a fork.
Boil the potatoes, cool, and smash down with your fist. Sear them in the butter and oil in a saute pan on medium heat until crispy, about 3 minutes on each side. Set aside.
While the fish is baking, prepare the fennel salsa. In a bowl, combine the chopped fennel, red onion, lemon juice, and olive oil. Season with salt and pepper, then set aside to let the flavors meld together.
For the vegetables, place the baby tomatoes, cauliflower florets, sliced carrots, and asparagus on a separate baking sheet. Drizzle with olive oil, then season with salt and pepper. Roast in the oven for 15-20minutes, or until the vegetables are tender and slightly caramelized.
To serve, place the veggies in the center of the plate, topping with a piece of halibut fillet on each plate. Spoon some of the fennel salsa over the fish, then serve with the roasted potatoes on the side.Enjoy your meal!