Preheat broiler to HIGH.
Place tomatoes, onion, and peppers on a baking sheet lined with foil. Place on a rack about 6 inches below the heating element. Roast for about 8 minutes, flipping the veggies halfway through. Keep an eye on them, don't let them burn!
Use a pair of tongs to transfer the roasted vegetables from the baking sheet into a blender or food processor. Add the cilantro, garlic, and salt and blend/process on Purée/High for about 30 seconds. Less for more chunky, or more for a smooth salsa.
Serve immediately warm, or store in an air-tight container and serve either chilled or room temperature.
