Dice bacon and fry until crisp. Drain and cool on paper towels.

In medium bowl, mix bacon, onion and mayonnaise.

Remove stems from tomatoes.

Place tomatoes stem side down on cutting board. Cut a thin slice off the top of each tomato.

With a small spoon, scoop out the pulp.

Invert tomatoes on paper towels 30 minutes to drain.

Fill tomatoes with bacon mixture.

Refrigerate several hours or overnight.