In a large bowl, combine ground beef, bread crumbs, egg, garlic, cilantro, chili powder, cumin, and oregano. Season mixture with salt and pepper, then form into meatballs about 2-inch in diameter.
In a large skillet over medium heat, heat 1 tablespoon oil. Add meatballs and cook to an internal temperature of 145 degrees, about 2 minutes per side. Remove from skillet and transfer to a plate while you make sauce.
Add remaining 1 tablespoon olive oil to skillet. Add onion and jalapeño and cook until soft, about 5 minutes. Stir in enchilada sauce, black beans, and corn and bring mixture to a simmer.
Return meatballs to skillet, tossing them in sauce. Top meatballs with cheeses and bake until beef is cooked through and cheeses are melted, about 15 minutes more.
Garnish skillet with avocado and more cilantro. Serve over rice OR with warmed tortillas and sour cream.