Preheat oven to 375°. Rinse inside and outside of fish well. Pat dry with paper towels. Place a large slice in the belly of the fish, and season inside and outside of fish with salt and pepper.
While fish is resting, combine garlic, ½ c of lemon juice, olive oil, and most of the cilantro. Once combined, rub the inside and the outside of the fish. Place fish on a baking sheet lined with parchment paper. Cover tightly with foil so steam doesn’t escape. Bake for 30 minutes.
Mix tahini and remaining ½ c lemon juice until creamy. If it is too thick, add water until creamy. Heat butter in pan and add pine nuts. Cook until toasted and nuts become fragrant.
After 30 minutes, uncover fish, and bake an additional 7-8 minutes until golden brown. Pour tahini sauce over fish and garnish with toasted pine nuts.