In a large pot over medium-high heat, brown the meat with the garlic, celery and onions. Remove the pot from the heat and drain off as much fat as you can. (Discard the fat once it cools.)
Return the pot to the heat and add the beef stock, tomatoes, tomato paste, parsley, oregano, salt, black pepper, cayenne, potatoes, carrots and green, red and yellow bell peppers. Stir to combine, then bring to a boil. Reduce the heat, cover the pot and simmer until the potatoes are tender but not overly mushy, 15 to 20 more minutes. The soup should be somewhat thick, but if you'd like it to be more "soupy," add 1 to 2 cups more broth OR hot water and heat through. Taste and adjust the seasonings, adding more salt, black pepper or cayenne if needed.