Combine red cabbage, red onion, and cilantro in a medium bowl. Whisk together lime juice, Dijon mustard, honey, salt, and ground pepper in a small bowl. Pour over the cabbage mixture and toss to coat evenly. Set aside to let flavors meld.
Pat the tilapia fillets dry with a paper towel. Mix lime juice, olive oil, garlic powder, cumin, cayenne pepper, and salt in a small bowl. Rub the mixture evenly over both sides of the fish.
Cook the Fish: Grill: Preheat a grill to medium heat and cook the fish for 3–4 minutes per side until opaque and flaky. Pan-Sear: Heat a nonstick skillet over medium-high heat. Add some oil, then cook the fish for 3–4 minutes per side. Bake: Preheat the oven to 375°F (190°C). Place the fish on a lined baking sheet and bake for 12–15 minutes.
Heat corn tortillas in a dry skillet over medium heat for about 30 seconds per side, or wrap them in foil and warm in the oven for 5 minutes at 300°F (150°C)
Divide the cooked fish evenly between the tortillas. Top with avocado slices, salsa, and a generous portion of Dijon cabbage slaw.
Serve immediately with extra lime wedges, if desired.
Notes
Alternative Fish Options: Swap tilapia for cod, halibut, or another mild white fish.
Low-Carb Option: Serve in lettuce wraps instead of tortillas.
Make it Spicier: Add sliced jalapeños or extra cayenne pepper to the slaw.