PREPARE ASPARAGUS by breaking off the bottom end about 2" from the end of each asparagus stalk, and it will naturally "snap" where the "woody" part ends, and discard. Rinse all the stalks in a colander under cold water.
In a 1 gallon Ziplock bag, combine the asparagus, red pepper, onion, oil, salt & pepper. Shake until mixed well, and evenly coated. Transfer to a 15x10x1" baking pan.
Bake at 450° for 10 to 15 minutes till golden brown, stirring once.