In a large, skillet cook eggplant slices in 1/2 inch of boiling water, covered, about 6 minutes or till tender.
Drain.
In the same skillet cook ground beef, onion, and garlic till beef is no longer pink.
Drain off fat.
Stir in tomato sauce.
Bring to boiling; reduce heat.
Simmer, uncovered, about 5 minutes or till of desired consistency.
Remove from heat.
Meanwhile, prepare sauce.
In a small saucepan melt margarine.
Stir in flour, salt, and pepper.
Stir in skim milk all at once.
Cook and stir till thickened and bubbly.
Remove from heat; set aside.
Spray a 10x6x2 inch baking dish with nonstick spray coating.
Arrange half of the eggplant in dish.
Spoon meat mixture atop, then top with remaining eggplant slices.
Pour sauce over all ingredients.
Sprinkle with Parmesan cheese.
Bake, uncovered, in a 325° oven for 30 minutes or till heated through and top is golden.