Prepare your slow cooker by creating a foil sling and collar for easy lifting and even cooking. Lightly spray the inside with cooking spray.
In a skillet over medium heat, warm the olive oil. Sauté the diced onion and red bell pepper for 3-4 minutes until they begin to soften. Add the minced garlic and cook for another 1-2 minutes until fragrant.
Stir in the tomato paste, cumin, oregano, and chili powder. Cook for 2 more minutes, allowing the spices to become aromatic. Remove from heat and let cool slightly.
In a large bowl, combine the torn bread pieces, rinsed black beans, and milk. Mash them together until well blended (your hands work great for this!).
Add the cooled onion mixture to the bread and bean mixture. Then, add the lean ground beef, shredded Mexican cheese, frozen corn, lightly beaten eggs, diced green chiles, chopped cilantro, salt, and black pepper. Mix everything thoroughly with your hands until just combined – try not to overmix!
Gently press the meatloaf mixture into an even layer in your prepared slow cooker.
Brush the top of the meatloaf with 1/4 cup of barbecue sauce.
Cover and cook on the LOW setting for 4 hours, or until the meatloaf is tender and fully cooked through (an internal temperature of 160°F or 71°C is ideal).
For a delicious caramelized topping: If you want to crisp up the top, carefully preheat your broiler. Using the foil sling, transfer the cooked meatloaf to a rimmed baking sheet, allowing any excess juices to drain back into the slow cooker.
Gently pull the foil away from the sides of the meatloaf and brush with the remaining 1/4 cup of barbecue sauce.
Broil for 3-5 minutes, keeping a close eye on it, until the barbecue sauce is bubbly and slightly caramelized.
Let the meatloaf rest for 15 minutes before slicing and serving. Enjoy your flavorful and easy meal!