Step 1

Preheat oven to 375 degrees. Spray a 9" X 13" baking pan with nonstick spray.

Step 2

Pulse cauliflower in a blender until reduced to rice-sized pieces, working in batches as needed.

Step 3

Bring an extra-large skillet sprayed with nonstick spray to medium heat. Season chicken with salt and pepper. Cook for about 4 minutes per side, until cooked through. Transfer to a cutting board.

Step 4

Remove skillet from heat; clean, if needed. Re-spray, and return to medium heat. Add cauliflower pieces, broccoli, onion, and celery. Cook and stir until partially softened, 8 - 10 minutes. Transfer to a large bowl.

Step 5

Chop chicken into bite-sized pieces, and add it to the large bowl. Add garlic powder, and mix well.

Step 6

To make the sauce, in a nonstick pot, combine milk, cheddar cheese, flour, and cheese wedges, breaking the wedges into pieces as you add them. Set heat to medium low.

Step 7

Stirring frequently, cook until smooth and uniform, about 4 minutes.

Step 8

Add sauce to the large bowl. Stir well. Transfer mixture to the baking pan, and smooth out the top.

Step 9

Bake until hot and bubbly, 20 - 25 minutes.

Step 10

Let stand for 5 minutes before slicing.