Place first 4 ingredients on a broiler pan, and broil 10 minutes or until tomatoes are tender and onion is slightly blackened. Cool 5 minutes.
Core tomatoes; discard cores. Coarsely chop tomatoes, peppers, chiles, and onion; place in a bowl. Add cilantro, oil, salt, and black pepper; toss gently.
Place salmon, skin side down, on grill rack. Grill 10 minutes or until fish flakes easily when tested with a fork. Top with about 2 tablespoons salsa; garnish with thyme, if desired.