Heat oven to 350°. Spray 1 1/2-quart casserole with cooking spray.
Melt butter in 3-quart saucepan over medium heat. Cook carrots, onion and mushrooms in butter about 5 minutes, stirring occasionally, until mushrooms are tender.
Stir in flour and salt. Gradually add milk, stirring constantly. Cook and stir until mixture is bubbly; remove from heat. Stir in cheese, peas and tortellini. Spoon into casserole. Sprinkle with crackers.
Bake uncovered about 15 minutes or until edge begins to bubble.