Cook rice according to package directions if using.
Wisk together JUSTEGG and garbanzo bean flour and set aside for 15 minutes before using.
If using shitake mushrooms saute in a large skillet for 2 minutes. Add napa cabbage and continue to saute for another minute. Remove vegetables from heat, set aside.
Prepare gravy in a small saucepan by heating all ingredients except cornstarch until boiling. Whisk together cornstarch with 3 Tbsp water to combine. Whisk mixture into boiling broth and continue to whisk until it thickens slightly about 2 minutes. Set aside.
Add 1/2 tsp sesame oil, 1/2 Tbsp vegan oyster sauce, 1/2 Tbsp mirin, and 1 Tbsp tamari to JUSTEGG, whisk to combine. Stir in all the vegetables except green onion.
Heat a large skillet over medium heat with a little oil. Using a 1/2 cup measuring cup, scoop JUSTEGG mixture into the pan, (cooking 2 to 3 at a time).
Spread the vegetables out slightly, then as JUSTEGG cooks slightly, bring the sides in with a spatula to form a circular omelet. Cook 3 minutes, flip and cook 2 more minutes. Sprinkle with black salt if desired.
Serve over rice, smothered in gravy then sprinkle green onions.