To a large skillet set over medium high heat, add the ground beef, onion, and pepper. Cook, stirring often, and breaking up the beef as it cooks.
Once the meat's completely browned, drain off the excess grease.
Add the condensed soup & milk to the skillet, and stir together to evenly combine the mixture. Remove the skillet from heat and set aside.
In a medium sized mixing bowl, add the bisquick & water and whisk them together just until evenly combined.
Lightly spray the crock of the crockpot with non stick cooking spray. Using a spatula scrape the mixing bowl to transfer the batter into the crockpot, spreading it out into an even layer.
Add the ground beef mixture into the crockpot (yes, on top of the batter), and spread it out as evenly as possible into an even-ish layer- doesn't have to be perfect. Sprinkle the shredded cheddar cheese evenly out overtop.
Add the lid to cover, and cook the casserole on HIGH for 3-4 hours, or until the batter has risen up and cooked through.
Serve the casserole topped with your favorite burger toppings and enjoy!