Pound round steak until very thin. Rub olive oil into steak. Sprinkle evenly with garlic salt and pepper. Layer carrots, zucchini, and cheese down the center of the steak lengthwise.
Roll up steak from the long side. Tie together with four pieces of string. Use a meat rack if you have one that will fit. Place meat in crockpot and cover with spaghetti sauce. Cover and cook on Low 7-9 hours (High 3-4 hours).