Preheat your Spark Grill to 600˚F, or preheat a regular grill to high heat.
Rub a thin layer of oil over the tomatoes and peppers. Place the peppers and tomatoes directly on the grill grates. Cover and cook, turning the vegetables occasionally, until they’re blistered and blackened (the tomato skin will start to slip off), about 6-8 minutes for the tomatoes and 15-20 minutes for the peppers.
Let the vegetables cool, then peel off and discard the skins (don’t go crazy with the peppers—if some skin doesn’t come off it’s totally fine). Cut out the pepper cores and discard the seeds. Cut the tomatoes in half lengthwise and slip out the seeds.
Transfer the tomatoes and peppers to a high speed blender or food processor along with the rest of the ingredients. Season with salt and pepper. Process on high until smooth, stopping and scraping down the sides occasionally (or stirring with the tamper if using a high speed blender). Taste and season with more salt and pepper as needed. The sauce will be quite pourable at this point, but it will thicken up as it rests!