Preparation Stir 1 cup onion, 1/4 cup cilantro, oil, 3 tablespoons lime juice, orange juice, garlic, and oregano in medium bowl. Sprinkle fish with coarse salt and pepper. Spread half of onion mixture over bottom of 11x7x2-inch glass baking dish. Arrange fish atop onion mixture. Spoon remaining onion mixture over fish. Cover and chill 30 minutes. Turn fish; cover and chill 30 minutes longer. Whisk mayonnaise, milk, and remaining 2 tablespoons lime juice in small bowl. Brush grill grate with oil; prepare barbecue (medium-high heat). Grill fish with some marinade still clinging until just opaque in center, 3 to 5 minutes per side. Grill tortillas until slightly charred, about 10 seconds per side. Coarsely chop fish; place on platter. Serve with lime mayonnaise, tortillas, remaining 1 cup chopped onion, remaining 1/2 cup cilantro, avocados, cabbage, Salsa Verde, and lime wedges.
Preparation Stir 1 cup onion, 1/4 cup cilantro, oil, 3 tablespoons lime juice, orange juice, garlic, and oregano in medium bowl. Sprinkle fish with coarse salt and pepper. Spread half of onion mixture over bottom of 11x7x2-inch glass baking dish. Arrange fish atop onion mixture. Spoon remaining onion mixture over fish. Cover and chill 30 minutes. Turn fish; cover and chill 30 minutes longer. Whisk mayonnaise, milk, and remaining 2 tablespoons lime juice in small bowl. Brush grill grate with oil; prepare barbecue (medium-high heat). Grill fish with some marinade still clinging until just opaque in center, 3 to 5 minutes per side. Grill tortillas until slightly charred, about 10 seconds per side. Coarsely chop fish; place on platter. Serve with lime mayonnaise, tortillas, remaining 1 cup chopped onion, remaining 1/2 cup cilantro, avocados, cabbage, Salsa Verde, and lime wedges.