I have to apologize in advance; I don't really measure anymore when I cook. Since this is a new recipe, you won't be getting much measurement guidance. I know that's a pain, but it's the Italian side of me saying, "Do what you think tastes and looks good."
Set the broiler of your oven to high and heat a cast iron skillet on your stove. Pour a small amount of grapeseed oil into the skillet. As soon as the oil heats up (it will be fast), carefully lay the fish scale side down in the skillet. Salt and pepper the upper side and sear for about a minute. Next, put the pan on the top grate of your oven so that it's about 4-6 inches away from the element.
While the fish is under the broiler, mix the juice of one lime with chopped cilantro and a small amount of avocado oil. When the fish is one minute from finished (you'll see it pulling apart; flaking), slide the skillet out for a moment and brush on the cilantro/lime/oil mixture. Finish cooking the fish under the broiler for about a minute. Spoon the fish into a bowl (If it's cooked right, it will flake apart by the simple act of moving it from pan to bowl) and serve family-style with the tortillas, guacamole, and salsa.
*Half the total fat and almost all of the saturated fat is from the avocado. Halve or omit if desired. Also, if you are cooking for yourself, you may find a full filet to be too much to eat all at once, so you can reduce these numbers further by halving the fish or just save half for lunch the next day. Cod is high in protein, so be careful. Remember, excess amounts of any macronutrient--including protein, will be stored as fat. So, don't eat this and then have a protein shake if you're trying to lose weight.
Based on these 3 ingredients and the oils (mango salsa, salt, pepper, and cilantro not included):
1 Cod fillet (231 g)
1 Half Avocado