Heat 1 tbsp of oil in a heavy-bottomed saucepan.
On medium flame, saute 1 large minced onion and garlic until fragrant. (You could also brown the onions first then add the garlic if you want a stronger Indian flavor.)
Add the grated ginger, green chilis and 1 large chopped tomato and let it cook for around 3-4 minutes.
Add 1 tbsp of soy sauce, 1 1/4 tsp of curry powder and 1/8 tsp of black pepper, then add in the cooked mung beans, mix it around and saute for 2-3 minutes. [This is why the dish's name literally means sauteed mung beans!]
Add 3 cups of water and 2/3 cup of coconut milk. Increase the flame to high and bring this to a boil, then let it simmer for around 10-15 minutes. You want the flavor of the spices and coconut milk to really get into those beans!
Add in the chopped onions and tomatoes and cook for around 2 minutes.
Add in your leafy greens and cook until desired doneness.
Add the fish sauce (if using) and adjust the consistency and seasonings to your taste. Do you like it thicker, soupier, creamier/more coconuty, maybe with more curry powder, black pepper or salt? Then you can cook it for longer or add coconut milk to make it thicker, or add water to make it thinner. If you are adding curry powder, cook it for a few minutes more. Curry powder that's "uncooked" is a little raw and harsh in flavor.
Serve with a bowl of rice. Brown rice tastes awesome with this dish!