Step 1: In a medium skillet set over medium-high heat, add the lean ground beef and cook for about 5-7 minutes. Break it up as it browns until there's no pink remaining. Drain any excess fat and transfer to the slow cooker.

Step 2: With the ground beef in the slow cooker, add the cream of mushroom soup, shredded cheddar cheese, uncooked shell pasta, milk, onion powder, kosher salt, and freshly ground black pepper. Stir everything together thoroughly.

Step 3: Place the lid on the slow cooker and set it to cook on high for approximately 3.5 hours. During the last half-hour, stir gently and check the pasta's doneness.

Step 4: Once cooked, ladle the dish into bowls and garnish with fresh chopped parsley or a dollop of sour cream. Serve hot.