Combine first 4 ingredients in a large bowl; stir well. Spoon half of mixture into a greased 8-inch square baking dish. Combine asparagus and pimiento; stir gently. Sprinkle over mixture in baking dish. Spoon remaining turkey mixture on top. Cover and bake at 350° for 35 minutes; uncover. Sprinkle with onion rings and bake, uncovered, an additional 10 minutes. Serves 4.