Here's a shot of Hugo brushing the marinade on the fish fillet, before it goes in the horno.
He says the secret is to brush the mayonnaise on first - para sellarlo (to seal it). Then brush on the seven other (secret) ingredients,
Also be aware - this fish is only prepared for comida, not usually available after 4 pm. In the future, he will be using the oven to make things like birria and costillas (smoky ribs).