Heat oven to 375°F. Spray 12x8-inch (2-quart) glass baking dish with cooking spray.
In 2-quart saucepan, cook Alfredo sauce, peas and mushrooms over medium heat until bubbly. Remove from heat. Gently stir in salmon and pimientos. Pour into baking dish.
If using crescent rolls: Unroll dough into 2 long rectangles. Press edges and perforations to form 1 rectangle. If using dough sheet: Unroll dough.
Place dough over salmon mixture in baking dish.
Bake 12 to 18 minutes or until crust is golden brown.