Brown the Beef: In a large skillet, cook the 1 lb ground beef over medium heat until browned, breaking it apart with a spatula as it cooks. Once browned, drain any excess fat and set the beef aside.
Prepare the Soup Base: In the slow cooker, add the cooked ground beef, 1 diced medium onion, 4 cups of cooked pinto beans (or 2 cans, drained and rinsed), 1 can (10 oz) of diced tomatoes with green chilies (such as Rotel), and 1 can (4 oz) of diced green chilies. Stir to combine.
Add the Liquid and Seasonings: Pour in 2 cups of beef broth and add 1 teaspoon of chili powder. Stir well to mix everything together. The chili powder will add a nice kick to the soup while complementing the other flavors.
Cook the Soup: Cover the slow cooker and cook on low for 6-8 hours or on high for 3-4 hours, until the soup is heated through and the flavors have melded together. The pinto beans should be tender, and the soup should have a nice, rich texture.
Serve: Once the soup is ready, taste and adjust the seasoning with additional salt, pepper, or chili powder if desired. Serve the soup hot, garnished with your favorite toppings, such as shredded cheese, sour cream, or chopped cilantro.
