To Make Cheese Spread: In small to medium bowl, warm water and bouillon in microwave just until hot. Stir until bouillon is completely dissolved. Add rest of ingredients, and stir and whisk until very creamy. Cover until needed. Chill if not using until later.
To Make Optional Secret Sauce: Add all ingredients into a small bowl and whisk to completely mix. Store the same way.
To Make Burgers: Divide hamburger into thirds and make 3 thin patties. Top with veggies, pressing into the meat, and season with salt and pepper.
Heat griddle over medium heat and place patties meat side down. Press tops well to smash burger, especially edges, and smash the veggies into the meat better. Fry burgers until meat is nicely browned on the bottom. Turn, use two spatulas if needed, scraping underneath WELL to get the "skin" of the meat from the grill.
Top with thinly sliced roast beef and shredded cheese. Add a little water next to each burger and cover with dome lids to melt cheese and cook the veggies.
If room on the griddle, or in separate pan or under the broiler, spread insides of buns with butter and toast buttered sides.
When burgers are done, remove from the griddle getting the goodies underneath, and place onto bun bottoms. Spread top buns with cheese sauce or optional mayo sauce, place on tops and dig in! Enjoy!