To make the marinade, stem and deseed the guajillo, pulla, and chile de arbol (discard stems and seeds). Place chiles in a large bowl and fill with warm water to just cover. Let soak until completely soft, 15–20 minutes.

Heat olive oil in a Saute Pan over medium-high and add the sliced onions. Fry until crispy, then transfer onions to a paper towel-lined plate and allow oil to cool slightly in Pan.

Pour half of the oil into a bowl to reserve for marinade. Heat remaining oil over medium-low and add annatto seeds. Cook until the oil is fragrant and turns an orange-red color, 2–3 minutes. Remove from heat and let cool.

Transfer cooled annatto oil mixture, raw and fried onions, and garlic to a blender and blend until smooth. Drain chiles and discard soaking liquid. Add chiles and vinegar to blender and purée. Slowly stream in the remaining oil from frying the onions and blend until smooth. Taste and season with salt. Makes about 1 cup and will keep in the fridge for up to 3 days.

Prepare a grill for high heat. Spray both sides of the Fish Basket with non stick cooking spray, or brush with vegetable oil. Brush marinade over the butterflied flesh of the fish (not the skin).

Grill fish starting skin-side down, until the edges of the flesh of the fish start to become white and the flesh becomes firm, about 5 minutes. Flip to flesh-side down and cook until flesh is opaque and flaky, 3–5 minutes more. Carefully remove from fish basket and serve skin-side down with your favorite tomatillo salsa.