Place pork belly, 2 cloves of garlic, and salt in a pot and add water, enough to just cover the pork. Bring to a boil and reduce to the simmer.
Continue to cook until the pork is fork-tender, about an hour.
Drain the pork
Measure 1/2 cup of pork stock and reserve the rest for future use.
Pat the pork dry with paper towels and cut into 2-inch pieces.
Fill a wok or a pot with at least 2 inches deep of oil and heat the oil.
Deep fry pork in small batches until brown.
Fish out with a strainer and place on a platter lined with paper towels.
Heat oil in a pan over medium-high heat.
Saute onions until fragrant and softened about 5 minutes.
Add the rest of the garlic and saute until lightly browned about 2 minutes.
Add tomatoes and saute until softened, about 5 minutes.
Add bagoong alamang, 1/2 cup pork stock, and chilies.
Bring to a boil and simmer for 5 minutes.
Add pork belly and combine well.