Place asparagus on a large baking sheet and spray spears with cooking spray. Sprinkle with desired amount of salt and pepper. Roast in oven for 20-25 minutes, depending on the thickness of your asparagus. You want them tender but not shriveled. Remove from oven and set aside.
Add butter to a small skillet and cook over medium heat for 4-5 minutes, stirring the butter or shaking the pan occasionally. (If you're using a stainless steel skillet, you'll see the color start to change to an amber color.) Immediately remove from heat and stir in the soy sauce and balsamic vinegar. Pour over asparagus and toss to coat. Serve warm.