Preheat the oven to 400°F with a rack in the center position.
In a small bowl combine the fish sauce, brown sugar, sriracha, red pepper flakes, sesame oil and vinegar.
In a large bowl toss the Brussel sprouts with 2 tablespoons of the sauce.
Transfer the Brussel sprouts to a rimmed baking sheet and spread out. Bake for 12 minutes. Turn the broiler on to high. Broil until browned and crispy, about 3 minutes.
Toss with remaining sauce and herbs, if using.
