Lightly toast bread. Cut each slice into 4 squares*. Chop green onion tops and bacon. Combine with just enough mayonnaise to bind. Season with pepper.
Cut ends off tomatoes and slice. Spread bacon mixture on toast squares and top with tomato slices. You can make these several hours ahead and refrigerate. Make a lot, they will go fast!
Notes
*If you want to get fancy, cut bread into shapes or circles with a cookie or biscuit cutter