1. Preheat oven to 400°.
2. Cook pasta in boiling water 6 minutes. Drain and rinse with cold water; drain. Combine pasta, ham, and peas in a large bowl.
3. Heat a medium saucepan over medium heat. Coat pan with cooking spray. Add onion to pan; cook 4 minutes, stirring frequently. Add milk; bring to simmer. Remove from heat; stir in cheeses, salt, and peppers. Pour cheese mixture over pasta mixture; stir to coat. Spoon pasta mixture into a 13 x 9–inch baking dish coated with cooking spray.
4. Place bread in a food processor; pulse 10 times or until coarse crumbs measure 1 1/4 cups. Combine breadcrumbs and butter in a bowl. Arrange breadcrumb mixture evenly over pasta mixture. Bake at 400° for 20 minutes or until lightly browned.