Stir 1 cup onion, 1⁄4 cup cilantro, oil, lime juice, orange juice, hot sauce, garlic, and oregano in medium bowl.
Sprinkle fish with sea salt and pepper.
Spread half of the onion mixture over the bottom of a 9" × 13" glass baking dish.
Arrange fish atop onion mixture. Spoon remaining onion mixture over fish.
Cover and chill for about 1 hour, flipping halfway through.
Grill fish on medium-high heat until just opaque in the center, 3–5 minutes per side. Lightly char the (coconut or cauliflower) tortillas.
Chop the cooked fish, and place on a serving platter with tortillas, remaining 1 cup chopped onion, remaining 1⁄2 cup cilantro, avocados, red and green peppers, cabbage, salsa, and lime wedges.