Heat a 10-inch cast iron pan over medium-high heat. Add ground beef and onion. Break ground beef apart as it cooks.
When there is no more pink in the ground beef, add chili seasoning and water. Simmer for 1 minute. Add remaining ingredients and simmer for 3 minutes.
In a medium bowl, mix together cornmeal, flour, sugar, baking soda, and salt.Add eggs, buttermilk, butter, and the diced jalapeno. Mix.Stir in half the cheese.
Spoon cornbread mixture over filling. Sprinkle the remaining cheese on top and arrange the jalapeno slices on top of the cheese.Place pan on a rimmed baking sheet in case there is any overflow.
Bake for 35 to 40 minutes. Check it after 25 to 30 minutes and if it is getting brown on top, place a piece of aluminum foil loosely on top of it.Note: Check to make sure the bottom of the cornbread layer is set before you take it out of the oven. It may need an extra 5 minutes or so to fully cook the cornbread.