Preheat oven to 350F. Whisk flour and 1/2 cup milk in saucepan until smooth. Gradually whisk in remaining milk. Bring to a boil over medium heat, whisking constantly, and boil 1 minute, or until thickened. Remove from heat; stir in pesto, Parmesan, salt and pepper. Reserve 1 cup while sauce.
Warm oil in large nonstick skillet over medium-high heat. Add chopped asparagus (not tips) and cook, stirring often, 5 minutes, or until tender. Add garlic; cook, stirring, 1 minute, and season to taste with salt and pepper. Remove from heat.
Coat 13x9-inch baking dish with cooking spray. Place layer of noodles in dish, overlapping slightly. Layer with half the cooked asparagus, 3/4 cup cheese and half the sauce. add another layer of pasta, remaining sauce, remaining cooked asparagus and 3/4 cup cheese. Top with layer of noodles, then reserved 1 cup white sauce. Arrange reserved asparagus tips over the top and sprinkle with remaining cheese.
Bake, uncovered, 35 to 40 minutes, or until golden. Let stand 10 minutes; serve with additional grated Parmesean cheese, if desired.