HEAT oven to 350ºF.
WHISK eggs and pepper until well blended.
HEAT dressing in large ovenproof nonstick skillet on medium heat. Add prosciutto; cook 2 min., stirring constantly. Stir in asparagus; cook and stir 2 min. Add spinach; cook 1 min. or just until wilted, stirring frequently. Stir in onions and cheese.
ADD eggs; stir. Cook on low heat 5 min. or until bottom is set but top is still runny, lifting sides of frittata occasionally to let uncooked mixture run underneath. Place in oven.
BAKE 6 to 8 min. or until centre is set.
serving size = 1/8 recipe (97 g)