Cook the ground beef, onions, and seasonings:
Heat the olive oil in a large skillet over medium-high heat. Add the ground beef and salt; cook, breaking up the meat with a spoon, until it’s browned and cooked through, about 6 minutes.
Add the onions, garlic, and taco seasoning:
Stir in the chopped onions, garlic, and taco seasoning. Cook, stirring often, until the onions are softened, about 3 minutes.
Add ingredients to the slow cooker:
Transfer the beef mixture to a 6-quart slow cooker. Stir in the chopped potatoes, kidney beans, corn, diced tomatoes, cream of chicken soup, and diced green chiles. Press the mixture into an even layer. Cover and cook on HIGH, stirring occasionally, until the potatoes are tender, 3 to 4 hours.
Top with cheese:
Sprinkle the shredded Cheddar-Jack cheese evenly on top of the casserole. Cover and cook on HIGH for about 15 minutes, or until the cheese has melted.
Serve with sour cream and cilantro:
Once ready, serve the casserole with a dollop of sour cream and a sprinkle of fresh cilantro leaves.