Heat a large skillet over medium heat. Add the ground beef, onion, and garlic. Cook, breaking the meat apart with a wooden spoon, until the beef is fully browned and the onion is softened. Drain any excess fat using a colander.
Add the taco seasoning, black beans, corn, and diced tomatoes with green chilies to the skillet. Stir everything together and cook for 3 to 4 minutes, allowing the flavors to combine. Remove from heat.
Pour half of the salsa and half of the broth into the bottom of the slow cooker. Spread it evenly to coat the bottom, which will prevent the ravioli from sticking.
Arrange half of the cheese ravioli in a single layer over the salsa mixture in the slow cooker.
Spoon half of the taco meat mixture evenly over the ravioli layer.
Sprinkle 1 cup of the shredded Mexican cheese blend over the meat.
Repeat the layers: add the remaining ravioli, followed by the remaining taco meat mixture, and top with the remaining 1 cup of cheese.
Pour the remaining salsa and broth evenly over the top of the layered ingredients.
Place the lid on the slow cooker. Cook on low for 2.5 to 3 hours, or on high for 1.5 to 2 hours, until the ravioli is tender and the sauce is bubbly and heated through.
If desired, stir in the sour cream to make the sauce extra creamy. Garnish with freshly chopped cilantro and serve warm.