Place avocados on the grill cut side down. Add the tomatoes along side. Grill for 4 to 5 minutes, turning the tomatoes once. The avocados should be nicely marked and the skin on the tomatoes shoud be blistered. Remove tomatoes from the grill. Turn the avocados peel side down a grill another couple of minutes. The avocado fruit will raise above the skin when they are done.