Evenly coat a 10-inch skillet with spray. Add zucchini, mushrooms, peppers and onion. Cover and cook over medium heat until peppers are crisp-tender. Set aside. Meanwhile, evenly coat 15 x 10 x 1 inch jelly roll pan with spray. Line with wax paper and spray again. Set aside.

In large mixing bowl at high speed, beat egg whites until stiff but not dry, just until whites no linger slip when bowl is tilted. In small mixing bowl at high speed, beat together yolks, flour, salt, if desired and pepper until smooth. Gently fold yolk mixture into beaten whites. Pour into prepared pan and gently spread evenly.

Bake in preheated 350°F oven until top springs back when lightly touched with finger, about 8 to 10 minutes. With spatula, loosen egg from sides of pan invert onto clean tea towel. Carefully pull wax paper. Trim all edges with serrated knife. Starting from long edge, roll up egg, rolling towel in with egg. Place wrapped roll seam-side down on wire rack until cook, about 30 minutes.

Carefully unroll cake and spoon 3/4 cup of the milk over egg. Sprinkle with reserved vegetables and 1/4 cup of the cheese. Reroll. Place seam-side down on shallow baking pan. Spoon remaining 1/2 cup milk and sprinkle remaining 1/4 cup shredded cheese over top. Bake in preheated 375°F until cheese is melted and heated through, about 10 to 12 minutes. Cut into 1 1/4-inch slices. Garnish slices with parsley sprigs, if desired.