Preheat oven to 400 degrees F. Slice the hamburger buns into small bite-size cubes then arrange in a single layer on a baking sheet. Drizzle with the olive oil and sprinkle with salt, to taste, then toss to coat evenly. Bake for 10-15 minutes until golden and crisp, then set aside.
In a large dutch oven, cook the bacon until crispy, then remove the bacon using a slotted spoon and drain the bacon fat. Set the bacon aside.
In the same pot, brown the ground beef over medium-high heat, breaking it up with a wooden spoon as you go until the meat is cooked and no longer pink. Transfer to a separate bowl and set aside. Drain any excess grease.
Melt the butter in the same pot over medium-high heat, then add the onion, celery, and carrots, cooking and stirring for 4-5 minutes until softened. Add the garlic and cook another 30 seconds.
Sprinkle the flour over the softened vegetables and stir it in, cooking for 1 minute. Add dried basil, parsley, and red pepper flakes.
Gradually whisk in the broth and milk, stirring to make sure there are no clumps of flour. Add the Worcestershire sauce, potatoes, and browned ground beef to the broth. Season with salt and pepper.
Once the soup comes to a boil, reduce the heat to a simmer and cook for 10-15 minutes, just until the potatoes have softened and are tender.
Sprinkle the cheese over the soup, stirring until it melts and combines with the broth, then remove from the heat.
Serve the soup in individual bowls, topped with the cooked bacon, hamburger bun croutons, chopped tomatoes, pickles, green onions, and additional cheese.