Preheat the oven to 350 degrees F. Line a baking sheet with parchment paper, then spray lightly with cooking spray.
Heat the oil in a medium skillet over medium heat. Cook the onions, stirring, until translucent, 7 to 8 minutes. Add the bay leaf, garlic, bell pepper, parsley and thyme and cook, stirring, until softened, about 5 minutes. Remove the skillet from the heat and let the onion mixture cool, then discard the bay leaf.
In a large bowl, combine the beef, eggs, breadcrumbs, Worcestershire sauce, 1/2 cup of the ketchup, the cooled vegetables, 2 teaspoons salt and 1 teaspoon black pepper. Use your hands to mix everything together. Transfer the mixture to the center of the prepared baking sheet and form into a loaf. Coat the meatloaf with the remaining 1/2 cup ketchup.?Bake until the meat loaf is firm, 1 to 1 1/2 hours. Let set for about 5 minutes before slicing. Slice into 8 pieces for thicker slices, 10 pieces for thinner slices.
Spread mayonnaise on 16 to 20 slices of bread and make sandwiches with the meatloaf slices.