Preheat oven to 350°℉. Lightly grease a deep 9x13" pan.
Combine cornbread mix, eggs & milk in a medium bowl. Set aside.
In a large skillet, brown meat & onion. Drain off fat if necessary.
Add in the salsa, corn, black beans taco seasoning & water. Mix well and cook over medium heat for 3-5 minutes.
Dump meat mixture into a 9x13" DEEP casserole dish (like a lasagna pan).
Top meat mixture with shredded cheese.
Spoon the cornbread over the top ensuring overall coverage. Smooth with spatula being careful not to pull the cheese layer up.
Bake, uncovered for 45 minutes.
Serve with green onions & sour cream. ENJOY!