Remove the stems from the tomatoes. Starting at the stem end and using small grapefruit spoon or paring knife, carefully hollow out each tomato, leaving 1/8-inch shell. Invert the tomato shells onto a paper towels to drain.
In a medium bowl, stir together the tuna, cottage cheese, celery, green onion, parsley, lemon peel and lemon juice.
Fill the tomato shells with the tuna mixture; place on a serving platter or tray. Serve immediately, or cover loosely and refrigerate up to 24 hours before serving. Tip: To level the bottoms of the tomatoes, cut a thin slice from the bottom of each.