Simmer zucchini in a small amount of water until tender, about 10 minutes. Drain and sprinkle with salt and pepper, set aside.
In a medium bowl, whisk egg yolks, sour cream and flour
In another bowl, beat egg whites until stiff; fold into the sour cream mixture.
Layer half of the Zucchini in a 12 x 7-inch baking dish, half of the sour cream mixture, and half the cheddar cheese; sprinkle with all of the crumbled bacon. Repeat layers of zucchini, sour cream mixture, and cheese.
In a small bowl, toss bread crumbs with melted butter; sprinkle over the top of the casserole.
Bake, uncovered, at 350 degrees for 20 to 25 minutes.