Heat the cooking oil in a pan.
Saute the onion and garlic.
Once the onion becomes soft, add the fish flakes and continue to cook in medium heat for 1 to 2 minutes.
Add the tomatoes. Stir and cook for 1 minute.
Put-in the mung beans. Stir, add the bagoong isda, and 1 cup water. Cover and cook for 15 to 18 minutes. Add more water if necessary.
Sprinkle some ground black pepper and then add the spinach. Stir.
Add more water (around 1 cup or more as needed). Let boil and cook for 5 minutes more.
Adjust the taste by adding more bagoong isda (only of needed).
Transfer to a serving bowl. Serve.
Serve and enjoy!