Pat the tilapia fillets dry with a paper towel and season both sides evenly with chili powder, sea salt, and black pepper.
Heat the olive oil in a medium non-stick skillet over medium-high heat until shimmering.
Place the tilapia in the skillet and sear for 3 to 4 minutes per side, until the exterior is golden-brown and the fish flakes easily with a fork.
While the fish is cooking, combine the shredded cabbage, lime juice, and chopped cilantro in a small bowl, tossing well to create a bright, acidic slaw.
Warm the corn tortillas in a separate dry pan or directly over a low gas flame for 30 seconds per side until soft and pliable.
Remove the tilapia from the heat and gently flake it into large, bite-sized chunks.
Assemble the tacos by dividing the fish between the tortillas, topping with the zesty cabbage slaw and fresh avocado slices.