Cut each asparagus stalk into 2-3 inch pieces on the bias. Place asparagus in a colander in the sink. When water starts boiling, pour over asparagus in sink, then immediately run the coldest water from the tap over the asparagus to stop the cooking. Tap the colander against the sink to shake off as much water possible. Transfer the drained asparagus to a bowl.
Place the sliced onions in a bowl of ice cold water and let them soak for 10-15 minutes to leach out some of the onion's "bite." Completely drain the onions and add to the bowl with the asparagus.
Combine vinegar, gochujang, gochugaru, maple syrup, sesame oil, soy sauce, and minced garlic in a small bowl.
Pour dressing over asparagus and onions. Toss asparagus and onions with the sauce in a bowl. Taste. Adjust seasoning if needed. You may need to add salt, vinegar for tartness, or gochugaru for heat.
Transfer Asparagus Salad to shallow serving bowl. Garnish with toasted sesame seeds.