Separate eggs. Let eggs and squash stand at room temperature for 30 minutes. Grease a 1-1/2-qt. souffle dish and lightly sprinkle with flour; set aside.
In a large bowl, combine the egg yolks, squash, butter, brown sugar, salt, orange zest, nutmeg and pepper.
In a large bowl with clean beaters, beat egg whites until stiff peaks form. With a spatula, stir a fourth of the egg whites into squash mixture until no white streaks remain. Fold in remaining egg whites until combined. Transfer to prepared dish.
Bake at 350° for 55-60 minutes or until the top is puffed and center appears set. Serve immediately.