Heat the oven to 400 degrees. Place flour, eggs, and panko into three shallow bowls. Season each with salt and pepper. Dip cauliflower in flour, then eggs, and coat with panko.
STEP 2
Fill a large skillet with 1/2-inch of oil over medium-high heat. Fry cauliflower in batches until golden brown, turning halfway. Transfer to a paper towel-lined plate.
STEP 3
Spoon sauce into a 9x13-inch baking pan. Sprinkle one-third of Parmesan. Layer half of the cauliflower and half of the mozzarella. Repeat layering with sauce, Parmesan, ending with a final layer of sauce and Parmesan.
STEP 4
Bake in the oven until cheese is golden and casserole bubbles, about 40 minutes. Cool slightly and top with basil before serving.