Prepare your slow cooker by lightly spraying the insert with nonstick spray or lining with a slow-cooker liner for easy cleanup.
In a large bowl, combine ground beef, French onion soup, breadcrumbs, grated Swiss cheese, chopped parsley, beaten egg, and salt and pepper to taste.
Mix the ingredients gently with your hands or a spoon until just combined. Avoid overmixing to keep the meatloaf tender.
Shape the mixture into a loaf about the size and shape of your slow cooker base. Transfer the loaf to the slow cooker, placing it in the center.
Pour any remaining French onion soup mixture over the top of the loaf for extra moisture and flavor.
Cook on low for 6 to 8 hours or on high for 3 to 4 hours. The meatloaf is done when internal temperature reaches 160°F and it feels firm to the touch.
About 30 minutes before the end of cooking, sprinkle additional Swiss cheese evenly over the meatloaf. Close the lid and let the cheese melt into a gooey finish.
When done, carefully lift the meatloaf onto a cutting board, slice, and serve hot. Spoon some of the cooking juices over each slice for extra flavor.
Notes
Store leftovers in an airtight container for up to 3-4 days. Reheat in the oven or microwave before serving.