Cut the stem of the cabbage out. The stem can be fairly tough so be sure to secure the cabbage well to avoid cutting yourself if it should roll.
Put the head of cabbage into a pot of boiling salted water. Boil for 5 minutes, rotating the cabbage halfway through. Remove and allow the water to drain out. The leaves will easily pull away.
Use a pairing knife to either cut the thick stem out or to shave it down making the leaves pliable.
In a large bowl, mix the tomato sauce, rice, green bell pepper, shallots, Worcestershire sauce, onion mix, seasonings, breadcrumbs, and egg together. Once combined, thoroughly mix the meat in.
Pour 1/2 can of the soup into the bottom of the slow cooker, spread it around.
Take about 1/3 cup of the mixture and place it in the center of a cabbage leaf. Fold in all sides as if you’re making a burrito to completely to enclose the filling. Place the cabbage roll seam-down on the soup the slow cooker.
Once you have your first layer of 6 rolls, pour half of the Rotel and remaining tomato soup from the open can over the top of the cabbage rolls.
Make the next 6 cabbage rolls, placing them on top of the previous layer. Once all of the rolls have been made, spread the remaining Rotel over them and the last can of tomato soup.
Cover and cook on low for 6-7 hours. A meat thermometer should read 160°F (but can be higher).
Sprinkle with parmesan cheese to serve.
Notes
Any ground meat will work: pork, sausage, chicken, turkey, or venison would make great substitutions.
Any leftover rolls should be placed in an airtight container and stored in the fridge for up to 4 days. You can reheat them in the oven or microwave.