Use tomatoes held at room temperature until fully ripe. Core tomatoes; cut in 1/2-inch chunks; set aside. Put bulgur and 1 cup boiling water in a medium heat-proof bowl. Let stand until bulgur is softened (about 15 minutes). Drain off any remaining water; return bulgur to bowl. Stir in onion, parsley, dressing, garlic, salt, coriander, and pepper. Toss to mix. Serve immediately or cover and refrigerate up to 2 days.