Remove the stems and remove the seeds of the bell peppers. Chop into quarters. Remove the stem of the habanero peppers. Add to a blender or food processor with 3 tomatoes, half a yellow onion, and either ½ cup of water or oil (depending on the type of sauce you want).
Blend or pulse to your desired consistency. Traditionally, the sauce is a bit coarse, so I pulse for a minute. If you want it smoother, you can also just blend it.
Transfer to a medium pot, and simmer on a low-medium flame for about 20-30 minutes. If you used oil, it will float to the top when its done cooking. If you just used water, the sauce will reduce by half to the desired consistency.
Turn off the stove when all the water has evaporated - store in an air tight container in a fridge and use for up to a week! If you want to store for longer, make sure to top off the sauce with oil so it avoids all contact with air.
If you're just using water, the sauce is done when the top starts forming large bubbles that pop - this means that most of the water has evaporated.
I keep my sauce seasoning free so it can take on flavors best suited to the dish I make with the sauce (e.g. more bold curry-type flavors for jollof rice, or more Italian flavors for pasta) - you're welcome to add seasoning to the sauce after it parboils!
You can store the sauce in the fridge for up to a week regardless of whether you use water or oil in the base. If you want to store it for longer, I suggest using oil, and topping off the container with a thin layer of oil to make sure it avoids all contact with air. This way, it'll last 2-3 weeks. You can also freeze this sauce for up to 4 to 6 months!