In a tall pan with the olive oil on medium-high heat, fry the diced onion until translucent, about 5 minutes.
Reduce to a medium heat, add the chopped jalapeño and garlic and continue cooking everything while stirring for another 2 minutes.
Chop the chipotles and add them along with the adobo sauce to the pan.
Add the butter, mayo and fish fillets to the pan.
Mix everything well for about 8 minutes until the fish is fully cooked.
To make the taco shells, fry the tortilla on a pan for about 2 minutes on each side on high heat. Let them cool in your desired shape and then fill them with the fish mix.