Layer the sliced onions on the bottom of a lightly greased slow cooker. Add the sliced potatoes on top and sprinkle with half of the salt, pepper, and garlic powder.
Crumble the raw ground beef evenly over the seasoned potatoes. Layer the sliced carrots and chopped celery over the meat, then top with the frozen peas.
Whisk the condensed tomato soup, undrained diced tomatoes, beef broth, and the remaining seasonings in a bowl until smooth.
Pour the tomato liquid evenly over the top layer in the slow cooker. Do not stir.
Cook covered on low for 6 to 7 hours, or on high for 4 hours, until the potatoes are tender.
