Cook the ground beef in a large pot over medium heat until completely browned, 7 to 10 minutes.
Drain as much fat from the beef as possible, add the onion to the beef; cook and stir until the onion is softened, about 5 minutes; add the garlic and stir until aromatic, about 1 minute.
Add the tomato paste, crushed tomatoes, onion soup mix, beef bouillon cubes, bay leaf, mixed vegetables, and stock/water to the ground beef mixture.
Raise heat to medium-high, and bring the mixture to a boil.
Stir the orzo pasta into the boiling liquid; cook until the orzo is tender, about 10 minutes.
Season with salt and black pepper to serve.
Notes
I use 7 cups home made stock + 1 cup water as the base of this soup.