Toss the cabbage, 4 tablespoons of the cilantro or parsley, scallions, vinegar, 1 teaspoon of the oil, and 1/4 teaspoon salt in a bowl. Refrigerate until serving.
In a small bowl, combine the remaining 1 tablespoon cilantro, mayonnaise, lime juice, chipotles (see note below), and garlic. Season with salt and pepper to taste. Refrigerate until serving.
Lay out fish fillets and pat dry with paper towels to prepare for the rub. Combine chili powder, coriander, cumin, 1/8 teaspoon salt, and 1/8 teaspoon pepper in a bowl. Brush fish with the remaining tablespoon oil, and rub evenly with the spice mixture (placing rub on top side only if fish still has skin).
Prepare your grill as desired for cooking fish. I use a charcoal grill and heat one side hot with a full layer of coals, and the other side with sporadic coals for lower heat.
Once coals are to your liking, grill fish with the skin side down first until you start to see it turn opaque, approximately 5 minutes. Turn fish over carefully and grill and addition 3-4 minutes. The skin is practically falling off the fish on its own here.
Remove fish from grill and cover with foil while you grill the tortillas.
Working in batches, grill the tortillas, turning as needed until warm and lightly charred, about 30 seconds. As the tortillas are done, wrap them in a clean kitchen towel or a large sheet of foil to keep them warm and soft.
Cut each fish filet into large chunks for filling the tacos. Smear each tortilla with some of the mayonnaise mixture and top with some of the cabbage slaw and pieces of fish. Serve with the lime wedges.