Prepare grill to medium-high heat. Clean the grill grates and brush with oil to prepare for grilling over medium heat.
Brush the tomatoes, the cut side of the onions and the peppers with olive oil. Grill over open flame (direct heat) for 8-10 minutes, until well charred and tomatoes are blistered.
Remove and allow to cool for 10-15 minutes, then drain any liquid that has seeped out of the tomatoes.
Remove stems, tomato peels and onion peels, discard.
Place grilled vegetables and all remaining ingredients into blender or food processor. Quickly blend until it reaches the thickness you prefer.
Pour into container and chill before serving to let the flavors blend together.
Notes
If it's raining, don't worry! Try charring your veggies in a grill pan on the stovetop, or roast them in the oven on a rimmed baking sheet.For a spicy salsa, you can either double the peppers, add a pinch of cayenne pepper, or dashes of hot sauce to your salsa!