Start the grill and make sure it gets up to temperature. If using an oven, preheat it to 425 degrees.
Place tomatoes, onion, peppers, and garlic on grill. (Using a grill wok for the smaller vegetables can be handy). A baking sheet will work for the oven just fine. Gently drizzle olive oil on the vegetables.
Roast on the grill until vegetables become tender and begin to show a nice color. (About 15 minutes).For the oven, roast veggies on baking sheet for 25-30 minutes.
Let roasted vegetables cool about 5 minutes. Then dice them up to your desired size. A food processor can also be used to achieve a less chunky consistency.
Combine all of the diced vegetables in a large bowl, add in lime juice and cilantro until desired consistency. Mix well.
Season with salt and pepper to taste. Allow salsa to chill for at least an hour before serving.