1. Heat oven to 400 degree F. Sprinkle fish with 1/8 teaspoon of the salt and the pepper. Place fish in glass baking dish. Cut one onion half into thin slices. Cut one line half into 4 thin slices. Arrange lime and onion slices on each fillet. Bake fillets 12 to 15 minutes or until just cooked and fish flakes easily with a fork.
2. Meanwhile, remove white pith from oranges; cut into segments, then cut each segment in half. Transfer orange pieces to small bowl. Mince 1 tablespoon onion from remaining onion half and squeeze 1 tablespoon lime juice from remaining lime half; add to orange pieces with avocado, jicama, cilantro, jalapeno, and remaining 1/8 teaspoon salt. Serve with baked fish. Makes 4 servings.