A fresh salsa of pineapple, red pepper, and ginger give these tacos a welcome kick, while grilled fish adds lightness to this taco dish.
Slice tops and bottoms off oranges, and discard. Using a paring knife, remove peel, pith, and outer membranes from oranges. Remove sections by cutting away from membranes, collecting sections and juice in a medium bowl. Squeeze any remaining juice from membranes before discarding.
Cut orange sections into 1/2-inch pieces, and add pineapple, red pepper, ginger, honey, 1/2 teaspoon salt, and crushed red-pepper flakes; toss to combine. Set aside.
Heat grill until very hot. Coat the fish with oil and cilantro; let rest about 10 minutes. Sprinkle with remaining 1/2 teaspoon salt and black pepper; place on grill. Cover, and cook several minutes until browned. Turn over, and continue cooking until fish is flaky and opaque throughout. Cut into pieces.
Place the tortillas on the grill just long enough to soften and brown slightly. Remove from heat, and fill with arugula, grouper, and pineapple salsa. Garnish with wedges of avocado, if desired, and lime wedges; serve immediately.
Select a grouper or other firm, white fish fillet that's not too thick; the fish will be more tender when cooked.