Cut the bottoms (not the buds) off the asparagus and arrange them in a single layer on a baking sheet. Spray the spears and sheet with cooking spray then sprinkle with salt and pepper. Give the pan a shake to distribute the seasoning and oil.
Bake for 12 minutes or until tender.
Melt butter in a small skillet over medium heat and cook for 3 minutes or until lightly browned, shaking pan occasionally. Remove from heat and stir in soy sauce and balsamic vinegar.
Drizzle balsamic sauce over the asparagus, tossing well to coat. Add a bit more fresh ground pepper if desired.
