Step 1Use a sharp knife (serrated is best) to cut a thin top from each tomato, just enough to remove the stem. Use a tomato shark (a small, round spoon-like tool with serrated edge) or the small end of a melon baller to remove and discard the seeds, leaving the shell intact. Lightly sprinkle the inside with salt.
Step 2Place the tomatoes, cut side down, on a baking sheet lined with paper towels. Allow them to drain for 4 to 6 hours or overnight in the refrigerator.
Step 3Mix the crumbled bacon, lettuce, mayonnaise, minced basil and green onion in a bowl. (This can be made several hours ahead and refrigerated.)
Step 4To assemble, place the tomatoes, cut side up, on a work surface. (To keep tomatoes stable, use a sharp knife to cut a small slice off the bottom, taking care not to cut through tomato). Fill each tomato with about 1/2 a teaspoon of the bacon mixture until just nicely mounded, using a small espresso or measuring spoon or pastry bag fitted with plain wide tip. Top each with a small basil leaf or minced basil, if using. Serve chilled.