Begin by heating a large skillet over medium heat. Add the lean ground beef and diced yellow onion. Cook until browned and onions are translucent, about 5-7 minutes.
Drain excess fat and transfer the beef and onion mixture to your slow cooker.
Add beef stock, frozen corn, fire-roasted diced tomatoes, crushed tomatoes, kidney beans, black beans, diced green chiles, taco seasoning, dry Ranch seasoning, and chipotle chili powder to the slow cooker. Stir thoroughly.
Season with Kosher salt to taste and squeeze in the juice of half a lime. Cover and set the slow cooker to low for 6-8 hours or high for 3-4 hours.
Once cooking time is complete, stir the soup and adjust seasoning if needed. Serve hot with toppings like shredded cheese, sour cream, or fresh cilantro.