In a mixing bowl, whisk together the honey, soy sauce, rice vinegar, garlic, ginger, red pepper flakes, sriracha, and sesame oil. I always taste it at this stage and adjust the heat level before it ever touches the shrimp. This base does double duty as both a marinade and the finishing glaze later.
Pour half of the sauce over the shrimp in a bowl or zip-top bag, saving the rest for the glaze. Toss well so every piece is coated, then let it sit in the fridge for 20 minutes. I don't go much longer than that, since the acid in the marinade can start to change the shrimp's texture if it sits too long.
Pat the marinated shrimp dry with a paper towel, then thread them onto skewers, piercing through both the head and tail ends so they lie flat. This little trick keeps the shrimp from spinning around when you try to flip them on the grill.
While the shrimp are marinating, pour the reserved sauce into a small saucepan with the cornstarch whisked in. Simmer over medium heat for about 3 to 4 minutes, stirring often, until it thickens into a glossy glaze. Set it aside off the heat until the shrimp are ready.
Brush the grill grates with neutral oil and heat to medium-high. Lay the skewers down and grill for about 2 minutes per side, until the shrimp turn opaque and pick up light char marks. Shrimp cook fast, so I stay right next to the grill the entire time.
Brush the reduced glaze generously over the hot shrimp right off the grill. Scatter scallions and sesame seeds on top before serving. I like to serve mine while the glaze is still warm and glossy, straight off the skewer.