Position an oven rack 6 inches from the broiler and heat the broiler. Arrange the roma tomatoes, white onion, and garlic on a foil-lined sheet; broil, turning once, until lightly charred and softened, 6–10 minutes.
Peel the roasted cloves. Transfer the roasted mixture to a blender with the canned chipotle chiles in adobo, adobo sauce (from canned chipotles), white vinegar, kosher salt, and water; blend until smooth or to desired texture.
Warm the vegetable oil in a medium saucepan over medium heat. Pour in the blended salsa and bring to a lively simmer; cook, stirring, 5–8 minutes until slightly thickened and the raw edge has cooked off.
Let cool 10 minutes, then taste and adjust seasoning. Serve at room temperature or chilled.