Heat a deep skillet over medium-high heat with EVOO. Add beef and deeply brown, 6-7 minutes. Add garlic, onion and mushrooms and cook until mushrooms are dark and onion is tender, 7-8 minutes. Season with salt and pepper, add the sherry and deglaze the pan, then reduce 1 minute. Add Worcestershire sauce and tomato sauce and stir to combine. Reduce heat to low and cook for 5 minutes more.
Pre-heat the broiler.
Spread rolls with softened butter and sprinkle heavily with parsley. Toast rolls until charred at edges. Top roll bottoms with sloppy mixture and shaved Manchego cheese, then set roll tops in place. Olé!