In a pot, boil the monggo beans in 5 cups of water over medium heat. Once it boils, cover the pot and reduce heat to low and let simmer until tender about 30 minutes.
Transfer the content of the pot in a deep bowl if using a stab mixer or in a blender, pulse to make a puree.
On the same pot, heat oil and cook the pork belly until browned and fat is rendered.
Add garlic, onion, and tomatoes and saute until tender. Add fish sauce and cook for another minute. If using salt, it may be added on the last step instead.
Add the pureed Monggo beans to the pot. Add 1-2 cups of water if it is too thick. When it starts to simmer, add the bitter gourd, celery and smoked fish. Let it simmer for another 2-3 minutes.
Lastly, add the pork rind (chicharon) and spinach. Season with salt if needed. Turn off heat.
Transfer to your soup bowl and serve while hot with rice.