Roma tomatoes, jalapenos, and onion are oven-roasted with garlic to make an intense, flavorful salsa.
Preheat broiler. Line a 15x10-inch baking pan with foil. Arrange roma tomatoes, onion, jalapeño peppers, and garlic in prepared pan. Lightly coat with cooking spray.
Broil 4 to 5 inches from heat 12 to 15 minutes or until charred, turning once. Cool slightly. Remove stems from jalapeño peppers (for a milder salsa, halve peppers, then remove and discard seeds) and peel garlic.
Using a slotted spoon, transfer vegetables to a food processor. Cover and process 15 seconds. Add cilantro, red wine vinegar, mustard seeds, salt, and black pepper to blender. Cover and process 15 seconds more or until salsa reaches desired consistency.
Serve immediately or cover and chill up to 3 days.