Preheat the oven to 350°F. Line a large rimmed baking sheet with aluminum foil.
In a large skillet, heat the olive oil over medium-high heat until shimmering. Add the onion, garlic, and a generous pinch each of salt and pepper. Cook, stirring occasionally, until softened and just starting to brown, about 8 minutes. Transfer to a large bowl and let cool.
Add the eggs, bread crumbs, milk, Worcestershire, 1 tablespoon salt, and ½ teaspoon pepper to the onion mixture and mix well. Add the ground beef and mix well. Transfer the meat mixture to the prepared baking sheet and, using damp hands, shape it into a 10 by 5-inch loaf. Drape the bacon slices over the meat loaf on an angle, gently tucking the ends of each slice under the meat loaf.
Bake the meat loaf for about 1 hour 10 minutes, until an instant-read thermometer inserted into the center registers 165°F. Let the meat loaf stand for 10 minutes, then cut crosswise into 1-inch-thick slices.
Spread mayonnaise on each slice of toast. Put a slice of meat loaf on 4 of the toasts. Top with the tomato jam and lettuce. Close the sandwiches and serve right away.
DO IT AHEAD The meat loaf can be refrigerated, covered, for up to 3 days. Reheat in a preheated 350°F oven before serving.