Preheat your oven to 350°F.
In a small bowl, mix together the cumin, chili powder, garlic powder, and salt.
Rinse the mahi mahi fillets and pat them dry with a paper towel. Rub the spice mixture all over the fillets, making sure to coat them evenly.
Heat the olive oil in a large skillet over medium-high heat. Add the mahi mahi fillets and cook for 2-3 minutes per side, or until they are cooked through and flaky. Remove the fillets from the skillet and let them cool for a few minutes.
While the fish is cooling, wrap the corn tortillas in foil and place them in the preheated oven for 5-7 minutes, or until they are warm and soft.
To make the sauce, whisk together the sour cream, mayonnaise, lime juice, garlic powder, salt, and black pepper in a small bowl.
Once the fish has cooled, use a fork to break it into bite-sized pieces.
To assemble the tacos, place a few pieces of mahi mahi on each warm tortilla. Top with shredded red cabbage, chopped cilantro, and diced red onion. Drizzle with the sauce and serve with lime wedges on the side.