Cook asparagus according to package directions, omitting the salt. Drain, reserving 3/4 cup cooking liquid. Place asparagus in a greased 11x7-in. baking dish. Top with peas, mushrooms and pimientos; set aside.
In a small saucepan, melt 3 tablespoons butter. Stir in flour until smooth; gradually add milk and reserved cooking liquid. Bring to a boil; cook and stir for 2 minutes or until thickened. Reduce heat; add the cheese spread, salt and pepper; stir until blended. Pour over vegetables. Melt remaining butter; toss with bread crumbs. Sprinkle over cheese sauce.
Cover and refrigerate for 8 hours or overnight. Or bake, uncovered, at 350° for 35-40 minutes or until bubbly. If refrigerated before baking, remove from the refrigerator 30 minutes beforehand.