Bring a pot of water to a boil; add the potatoes and cauliflower and cook at a boil until soft, about 20 minutes. Drain and transfer to a large bowl. Pour the milk over the mixture and mash with a potato masher until smooth.
Crumble the beef bouillon cube into the water; whisk until the bouillon is dissolved. Pour into a slow cooker. Add the stew meat, bacon, carrot, onion, garlic, and tomato to the slow cooker. Spread the mashed cauliflower and potato mixture over the meat and vegetable mixture. Sprinkle the Cheddar cheese over the top.
Set the slow cooker to Low and cook for 8 hours, or, if you prefer, at High for 4 hours.
