Heat oven to 350°F. Line a baking sheet with parchment paper.
In a bowl, sprinkle cumin, salt, and 1 teaspoon of tajin seasoning on the cod. Mix until cod is coated with spices. Place cod on lined baking sheet and bake for 20 minutes or until the internal temperature is 145°F.
Begin making sauce by combining mayo, Greek yogurt, lime juice, and 1 teaspoon of tajin. Stir well. If the sauce is too thick, add a teaspoon of water to thin it out if desired.
Assemble tacos by first heating the tortilla on a pan for 30 seconds on each side, next place cooked cod in a tortilla, followed by shredded cabbage, sliced avocado, and top with Greek yogurt sauce. Add a splash of hot sauce if desired. Enjoy!