How to Make It
In a medium saucepan, combine the soy sauce with the dashi powder, sugar and 3 cups of water and bring to a simmer. Cover and keep warm off the heat.
In a large nonstick skillet, heat 2 tablespoons of the oil. Add the onion and mushrooms, season with salt and cook over high heat until lightly browned, 5 to 6 minutes. Add the tofu and cook until lightly browned, about 1 minute. Add the spinach and cook just until wilted, about 30 seconds. Scrape the mixture onto a plate.
Heat the remaining 1 tablespoon of oil in the skillet. Add the chicken, season with salt and cook over high heat, stirring twice, until just white throughout, about 3 minutes. Return the vegetables and tofu to the skillet and cook, stirring, just until combined. Spoon the mixture into shallow bowls and add sushi rice. Ladle the broth on top and serve.
Dashi is a clear Japanese stock that's often made with dried bonito (tuna) flakes and water. It is available in powdered form at Asian markets. In place of the dashi and water called for here, you can use 1 1/2 cups of low-sodium chicken broth mixed with 1 1/2 cups of water.