Chipotles in adobo are a great way to add intense heat and a rich, sweet, smoky flavor to sauces and other dishes.
Preheat broiler. On a broiler-proof sheet pan, toss tomatoes with onion, oil, salt, and pepper. Broil until charred in spots, 15 to 20 minutes; cool.
Transfer contents of sheet pan to a food processor; add chipotles, cilantro, and lime juice. Pulse until combined but still chunky.