Using a fine mesh sieve, rinse the shrimp paste multiple times to reduce its saltiness and remove any impurities or foreign particles that may be present. Gently squeeze and set aside.
To reduce heat, you can blanch the chili peppers by soaking them in hot or warm water for about 5 minutes, then drain.
Brown the pork belly pieces over medium-high heat, adding a splash of water to help render the fat. Push the pork to the side of the pan. Discard excess fat and replace with regular oil, as desired.
In the same pan, reduce the heat to medium and add the garlic and onion. Sauté until they are softened, about 3 minutes.
Sauté the shrimp paste, spreading it out to prevent it from becoming too watery. Cook for about 2 minutes, while stirring constantly with the aromatics and pork.
Add the chili peppers and sauté for about a minute to develop a smoky flavor.
Add the tomatoes and sauté until they cook down and start to caramelize, adding more oil as needed. Season with ground pepper and sugar to balance the flavors. Turn off the heat.
Notes
Shrimp paste: This is fermented small shrimp with a strong umami flavor and aroma. It's also called bagoong alamang or salted shrimp fry available in Asian supermarkets.
Pork belly: You can use leaner options like pork shoulder or loin. If you want to leave it out, that's okay too.