In a small bowl, whisk the mayonnaise with the hoisin sauce, pickle relish, and lemon juice.
Combine flour, garlic salt, onion powder, salt, and pepper in a large zip-lock bag. Seal the bag closed and shake the mixture. Then add the fish in and continue shaking, making sure the fish is nicely coated in the mixture.
Place lightly beaten eggs in one large shallow bowl and place panko in a second. Dip the breaded fish in the eggs first followed by the breadcrumbs and place on a plate.
In a large skillet, heat vegetable oil to 350 degrees. Once heated, begin adding the fish and cook for about 3 minutes (1.5 minutes each side). Place fried fish on a paper towel-lined plate.
Add lettuce, scallions, and cilantro to corn tortillas. Top with fried fish and drizzle mayo/hoisin sauce over the top. Squeeze more lemon on top, if desired.