Preheat your oven to 375°F. In a skillet over medium heat, brown the ground beef and chopped onions. Season with salt and pepper to taste. Drain any excess fat.
Layer Ingredients: In a greased 9x9 inch (or small 9x13) casserole dish, layer the ingredients in the following order:
Sliced potatoes on the bottom.
The cooked beef and onion mixture over the potatoes.
Spoon the baked beans over the meat mixture.
Pour the condensed tomato soup evenly over everything (do not add water to the soup).
Cover the casserole dish tightly with aluminum foil or a lid. Bake for 30 minutes. Then, remove the cover and continue baking for another 1 hour, or until the potatoes are fork-tender and everything is thoroughly heated.
Let the casserole cool for a few minutes before serving.