Set the ovel to broil or grill, with a temperature of 500°F, 260°C, or gas mark 10.
On a sheet pan place the peppers and place them on the top rack. Once the skin starts to blister and burn, pull the sheet pan from the oven and rotate the peppers so that a different side is facing the heating element. Remove from the oven when all of the skin has been burned.
While the peppers are cooking fill a bowl with ice water. Once the peppers are done submerge them in the cold water. Slide off the burned skin and place the peppers into the blender or food processor.
In a sauté pan add the oil and onions. Cook on medium high heat until the onions start to turn translucent add the garlic and cook until soft.
Add the cooked garlic and onions to the blender or food processor along with the rest of the ingredients. Blend until the mixture is nice and smooth.