How to Make It
Preheat grill to high.
Place tomatoes, chiles, and onion on grill rack coated with cooking spray; grill 10 minutes or until vegetables are blistered and charred in spots on all sides, turning occasionally. Remove from grill; cool 10 minutes. Stem and seed chiles; discard stems and seeds.
Place tomatoes, chiles, onion, and garlic in a blender; blend until almost smooth. Stir in salt.