Okinawan Taco Rice

Name: Okinawan Taco Rice
Ingredients: 2 cups sushi rice; 3½ cups water , divided; 2 tablespoons vegetable oil; 1 onion, chopped fine; 1 pound 90 percent lean ground beef; 1 (1-ounce) packet taco seasoning; 2 tablespoons ketchup; 2 tablespoons mirin; 2 tablespoons soy sauce; 1 teaspoon Hondashi instant dashi; 4 ounces Monterey Jack cheese , shredded (1 cup); 2 cups shredded iceberg lettuce; 1 avocado , halved, pitted, and cut into ½-inch pieces (optional); ½ cup jarred tomato salsa; Lime wedges