Place the butter in a large nonstick pan and heat over medium-high heat. When melted, add onion and bell pepper. Cook 3 minutes and then add green onion and jalapeno. Cook another few minutes or until onions and peppers are soft.
Drain any liquid from crawfish and add to pan along with creole seasoning. Remove from heat and set aside.
In a large bowl, whisk together cornmeal, baking powder, salt, and baking soda.
Add cheddar cheese, canned corn, milk, oil, and eggs. Add onion/crawfish mixture. Stir to mix well.
Transfer mixture to a greased 10-inch cast iron skillet. Bake for 35 to 45 minutes, or until golden on top and set in the middle.
If you don't have a 10-inch cast iron pan, you can use a 9x13-inch baking pan.