Set oven rack about 6 inches from the heat source and preheat the oven's broiler. Line a baking sheet with aluminum foil and brush with olive oil.

Spread tomatoes, onion, garlic, and jalapeño peppers onto prepared baking sheet.

Cook under the preheated broiler for 5 minutes. Turn the baking sheet and continue broiling until vegetables are charred, about 5 minutes more. Cool slightly.

Remove garlic from skins; discard skins.

Blend tomatoes, onion, peeled garlic, jalapeños, any accumulated juices from the baking sheet, cilantro leaves, lime juice, cumin, cayenne pepper, and oregano in a blender until salsa is smooth. Transfer to a bowl, cover with plastic wrap, and refrigerate until flavors blend, at least 2 hours. Season with salt and black pepper.