Rinse the pinto beans under cold water and sort through them to remove any debris or damaged beans. Soak the beans in water overnight or perform a quick soak by boiling them for 2 minutes and letting them sit for an hour.
In a large skillet, heat the olive oil over medium heat. Add the diced onion and sauté for 3-4 minutes until translucent.
Add the minced garlic, ground beef, cumin, chili powder, salt, and pepper to the skillet. Cook until the beef is browned and no longer pink, about 5-7 minutes. Drain excess fat.
In the slow cooker, combine the soaked pinto beans, cooked beef mixture, diced tomatoes with green chilies, canned green chilies, and beef broth.
Stir all the ingredients together in the slow cooker. Cover and set the slow cooker to low for 6 hours.
After 6 hours, taste and adjust seasoning if necessary. Serve hot, garnished with fresh cilantro or a squeeze of lime if desired.