Preheat broiler, and on a small cookie sheet, place tomatoes flesh side up, jalapenos cut side down, and whole garlic cloves. Spray with olive oil and season lightly with salt and pepper.
Place sheet under broiler for 5 minutes, checking periodically that the garlic and jalapeños aren't burning. Pull them when the garlic has turned a golden color, and there is char on the skins of the jalapeños.
The tomatoes will take longer to char on their flesh side, so let them stay under the broiler longer until you see the char happening, about 5 minutes longer.
Remove from the oven, and finely chop the garlic and jalapeños. When the tomatoes have cooled enough to handle, roughly chop, and add all veggies to a small bowl. Season with salt to taste.