Heat oil in large non-stick skillet over medium-high heat. Add onion, over, and cook for 3 minutes. Uncover and cook 10 minutes or until golden brown, stirring frequently.
Place pizza crust on a baking sheet. Top evenly with onion mixture; sprinkle with cheese. Top evenly with pear and prosciutto. Sprinkle with pepper. Bake for 12 minutes or until cheese melts. Sprinkle with nuts. Place arugula in a medium bowl. Drizzle vinegar over greens; toss gently to coat. Top pizza evenly with arugula mixture.