In a large skillet over medium heat, add the ground beef and chopped onion. Cook until browned, about 6-8 minutes, then drain excess fat.

Wash and thinly slice the potatoes into 1/8-inch thick rounds. Cover in a bowl to prevent browning.

Layer half of the sliced potatoes in the slow cooker, followed by half of the cooked beef and onion mixture, then a portion of cheddar cheese. Repeat layering with remaining ingredients.

In a mixing bowl, whisk together cream of mushroom soup, milk, garlic powder, salt, and pepper. Pour this sauce over the layered ingredients.

Cover the slow cooker and cook on low heat for 6 to 8 hours, until potatoes are tender and cheese is melted.

About 15 minutes before serving, sprinkle the remaining cheese on top and cover until melted.

Garnish with fresh herbs and serve warm.