Remove stems from tomatoes. To level bottoms of tomatoes, cut thin slice from bottom of each. Starting at stem end and using small spoon or melon baller, carefully hollow out each tomato, leaving 1/8-inch shell. Invert tomato shells onto paper towels to drain.
In small bowl, combine cream cheese and mayonnaise; blend well. Stir in cucumber, onions and dill; mix well.
Fill tomato shells with cream cheese mixture; place on serving platter or tray. Cover loosely; refrigerate at least 2 hours or up to 24 hours before serving. Store in refrigerator.