Preparing the Egg Foo Yong:
If using shrimp, peel, devein, and roughly chop.
In a bowl, whisk together the eggs and cornstarch.
Season the egg mixture with soy sauce, Maggie seasoning, and fish sauce.
Add the chopped green onions, bean sprouts, and chopped shrimp (if using) to the egg mixture. Stir to combine.
Let the mixture sit for 5 minutes.
Heat a cast-iron skillet over medium heat and lightly coat with cooking spray.
Ladle about 1/3 of the egg mixture into the skillet to form a cake. Repeat to make 3 cakes.
Cook on each side for 4 minutes, or until golden brown. Flip and cook the other side until golden brown.
Remove the egg foo yong cakes from the skillet and set aside on a plate, covered to keep warm.
Making the Gumbo Gravy:
Heat oil in a saucepan over medium heat.
Add flour and whisk continuously until smooth.
Cook for 20 to 30 minutes, stirring occasionally, until the roux turns a dark brown color and has a nutty aroma.
Once the roux reaches the proper color, gradually whisk in the vegetable broth until smooth.
Season with seasoning salt, bay leaves, celery seed, black pepper, cayenne pepper, minced green bell pepper, and minced garlic.
Simmer until the gravy thickens.
Remove from heat and cover to keep warm until ready to serve.
To Serve:
Place the egg foo yong cakes on a plate and generously spoon the gumbo gravy over the top. Serve hot over white rice.