In a large resealable bag combine soy sauce, vegetable oil, sugar, garlic, ginger, and pepper flakes. Adjust until blended.
Add asparagus and adjust until coated.
Allow to marinate at room temperature for at least 15 minutes but no longer than 1 hour.
Remove asparagus and do not discard marinade, Grill, watching closely, until tender and a little charred, 4 to 8 minutes.
Add sesame oil to marinade and adjust until combined. Pour into bowl or serving plate.
Add grilled or cooked asparagus to marinade and toss until coated. You can also carefully chop your hot asparagus before tossing again in your marinade. I lined the hot asparagus up on a cutting board and sliced it into 2 to 3 inch pieces before adding it to bowl with marinade.
Season with salt and pepper and sprinkle with toasted sesame seeds, if desired. I rarely do. Serve and enjoy!