Pat the cod dry and place in a shallow dish. Whisk together 2 tbsp oil, 1 tbsp lemon juice, 1 tsp paprika, 1/2 tsp cayenne, 1/2 tsp cumin, and salt to taste; pour over the fish and coat evenly. Marinate at least 30 minutes.
Make the creamy sauce by stirring 1/4 cup Greek yogurt, 2 tbsp mayonnaise, 1 tsp lemon juice, 1/2 tsp paprika, and salt to taste until smooth; set aside.
For the slaw, combine 1 cup shredded purple cabbage, 3/4 cup shredded carrots, 1/3 cup thawed corn, 2 tbsp chopped jalapeños, and 1/4 cup chopped cilantro. Stir in 3 tbsp Greek yogurt, 1 tsp lemon juice, and salt to taste until evenly coated.
Heat a skillet over medium-high heat. Add a little oil if the pan is dry, then sear the marinated cod for 3–5 minutes per side (or until cooked through and opaque). Transfer to a plate and flake into bite-sized pieces with a fork.
Warm or char 6–8 corn tortillas over an open flame or in a dry skillet until pliable and lightly charred.
Assemble tacos by placing flaked cod on each tortilla, adding about 1 tablespoon of slaw, drizzling with the prepared sauce, and garnishing with reserved jalapeños and cilantro.