Pat codfish filets with a paper towel to soak up any residual water, then season with salt, pepper, cumin, and tajín Clásico Seasoning.
Combine all ingredients for chili lime crema in a bowl and transfer to the fridge until ready to use.
Toss all ingredients for the crunchy slaw together and set aside until ready to assemble tacos.
Heat oil in a skillet over medium-high heat. Sear prepared cod filets on each side for 2-3 minutes. The fish should have a nice sear and start to flake when it's done.
Char tortillas over an open flame on the burner for about 30 seconds on each side, if accessible. Alternatively, heat a skillet over high heat and cook on both sides for 30 seconds. Stack tortillas on a plate and cover with a towel to keep warm.
To assemble tacos, stack two tortillas on top of each other. Spread a thin layer of chili lime crema on the bottom and top with a seared cod filet. Add a scoop of slaw on top and finish with a few pickled onions and chopped cilantro for garnish.