Step 1

In a medium bowl combine 1 cup of the chopped onion, 1/4 cup cilantro, olive oil, 3 tablespoons lime juice, orange juice, garlic, and oregano until combined

Step 2

Sprinkle fish with salt and pepper

Step 3

Spread half of the onion mixture in the bottom of a baking dish

Step 4

Arrange fish atop onion mixture

Step 5

Spoon remaining onion mixture over fish

Step 6

Cover and chill 30 minutes

Step 7

Turn fish; cover and chill 30 minutes longer

Step 8

Whisk mayonnaise, milk, and remaining 2 tablespoons lime juice in small bowl, set aside.Using a silicon grill brush, brush grill grate with olive oil; turn grill on to medium-high heat

Step 9

Grill fish with some marinade still clinging to it, 3 to 5 minutes per side, until fish easily flakes

Step 10

Grill tortillas until slightly charred, about 10 seconds per side.Coarsely chop the grilled tilapia; place on platter

Step 11

Serve with lime mayonnaise, tortillas, remaining 1 cup chopped onion, remaining 1/4 cup cilantro, avocados, cabbage, salsa verde or pico de gallo and lime wedges.