Rub cavity and skin of the fish with olive oil and garlic. Sprinkle with salt and red pepper flakes. Stuff cavity with sliced fennel and shallot. Layer slices of lemon on the skin of both sides of the fish and use kitchen twine to secure. Place in baking dish and surround with remaining fennel and shallots.
Cover with plastic wrap and allow to marinate in the refrigerator for an hour or two.
Preheat oven to 375ยบ.
Bake fish approximately 30 minutes until flesh is somewhat opaque but still very moist. Remove fillets and serve with additional lemon, olive oil, and red pepper, if desired.
Recipe by strawberryplum at http://www.strawberryplum.com/whole-roasted-branzino-with-lemon-fennel/