Start by steaming your veggies until tender. You can do this by steaming them in the microwave 3-5 minutes, or until tender. (You could do this two ways, either in a bowl with 1/4-1/2 cup water, covered with saran wrap and pierced with holes, or you could buy the steam-able frozen bags of veggies). Or you could lightly sauté the veggies in a large skillet until tender.
Preheat oven to 425 degrees. Spray a medium non-stick skillet with cooking spray. Pour egg whites into skillet, and place steamed vegetables, tomato slices, salt and pepper, and parmesan cheese over the top of the egg whites. Drizzle ketchup evenly over the top if desired (this becomes like the tomato sauce in a pizza). Place skillet in the oven for 20-25 minutes, or until the top becomes lightly golden brown (this may vary slightly based on the size of your skillet, but the egg whites should be firm to the touch). Remove from the oven and slide the pizza onto a plate. Slice into pizza slices, if desired and enjoy!