Mix rice, cornstarch, water, salt, and sugar in a bowl. Place plastic wrap over bowl and poke holes for ventilation. Cook on high for 90 seconds. Let cool for 5 minutes before handling.
Whisk 1 egg in a bowl and pour onto a greased microwavable plate (use oil or butter for added flavor). Place a paper towel over a plate and cook on high for 45 seconds. If the egg is runny, cook in 30-second intervals until rm. When the egg is fully cooked, carefully peel from the plate and cut into 1-inch rectangles.
Mash pitted avocado in a bowl. Apply butter or Crisco to hand to prevent rice from sticking. Compact 1/4 cup cooked rice in hands into football shape (see photo). Place egg and avocado on rice. Use soy sauce for dipping.