Preheat your oven to 375°F and spray a 9x13-inch casserole dish with non-stick cooking spray.

In a medium bowl, prepare the cornbread mix according to the package directions with eggs and milk, setting aside for later.

Heat a large skillet over medium heat, adding ground beef and diced onion, cooking until the beef is no longer pink and the onion is soft (about 8 to 10 minutes).

Carefully drain any excess fat from the skillet.

Return the beef and onion mixture to the skillet and add Ro-tel, pinto beans, corn, and taco seasoning, stirring until combined.

Spread the meat mixture into the prepared casserole dish in an even layer.

Pour the cornbread batter evenly over the meat mixture, spreading gently.

Bake uncovered for 40 minutes, until the cornbread is golden and a toothpick inserted into the center comes out clean.

Let the casserole rest for 10 minutes before serving.