Remove the seed from the red bell pepper. Set aside.
Peel the onions and chop them into small pieces.
Mince the garlic and set aside.
Place the red bell pepper, red chilis, garlic, and two cups of water into the electric chopper. Pulse one to two times. You don't want to blend spices.
Transfer the ingredients to a medium size pan and add the half cup remaining water and add the vinegar. Add the sugar and the salt. Turn the heat to medium. Mix until the sugar is dissolved. Let it boil
Meanwhile, mix the cornstarch and the water until smooth. Once the prepared mixture above boils, add the slurry and turn the heat to low until the mixture has a thick consistency.
Let the mixture cool down and transfer it to a container. This sauce tends to curdle, so you can reheat it in low heat for a few minutes to regain its smooth consistency.