Step 1

Preheat the oven to 400 degrees F (200 degrees C). Prepare a 1 1/2- to 2-quart casserole dish with cooking spray.

Step 2

Set aside 2 tablespoons of the cornbread mix and the white portions of the green onions for the filling.

Step 3

Prepare the cornbread topping: combine remaining cornbread mix with 1/2 cup water, Cheddar-Jack cheese, and green portions of green onions in a mixing bowl; stir to combine. Add additional water, 1 tablespoon at a time, until fully combined and a thick, spreadable batter forms. Set aside.

Step 4

Prepare the filling: heat a large nonstick pan over medium-high heat and add olive oil. Add chicken, carrots, mushrooms, bell pepper, onion, jalapeno, reserved white portions of green onions, Cajun seasoning, salt, and pepper. Cook and stir until chicken is no longer pink, 7 to 8 minutes. Stir in reserved cornbread mix. Add 1/4 cup water and bring to a simmer. Stir occasionally until slightly thickened, 1 to 2 minutes.

Step 5

Transfer chicken and vegetable filling to the prepared casserole dish. Top with cornbread batter and smooth with a spatula. Don't worry if layer is thin.

Step 6

Bake in the preheated oven until browned and bubbly, 20 to 25 minutes. Let rest for 5 minutes before serving.