Heat oven to 350°F.
In a large pot, steam cauliflower for 7 to 8 minutes and broccoli for 5 minutes, or until fork-tender. Set aside.
In a food processor or blender, mix together eggs, onion, soup and mayonnaise until smooth.
In a 13 x 9 x 2-inch baking dish, spread cauliflower in an even layer. Sprinkle with half the cheese and top with half of the soup mixture. Repeat layering with broccoli and remaining cheese and soup mixture.
Prepare stuffing mix following package directions. Spoon stuffing over top of casserole. Bake at 350°F for 45 minutes. Serve warm.