Mix all of the ingredients together in a medium bowl (for a chunkier sauce) or place in a blender and blend until smooth.
To make Tacos:
Spray a grill with cooking spray and heat over medium heat.
Season the fillets with lemon pepper and cook for approximately 15 minutes, turning once. Fillets should be white throughout and flaky but not overcooked.
Place 1/4 lb. halibut over 3 (slightly stacked) heated tortillas.
Add 1/4 cup cabbage and top with 1/4 cup creamy avocado sauce.
Repeat the process for the remainder of the ingredients.