In a small bowl or measuring cup, whisk together the chicken stock, soy sauce, rice vinegar, hoisin sauce, brown sugar, Sriracha, minced garlic, grated ginger, and cornstarch until the cornstarch is dissolved; set the sauce aside.
Pat the shrimp dry with paper towels to reduce splatter.
Heat the untoasted sesame oil in a large skillet over medium-high heat until shimmering.
Add the shrimp to the hot skillet in a single layer and cook 1–2 minutes per side, until the shrimp are opaque and just cooked through.
Quickly whisk the sauce again, pour it into the skillet, and stir constantly for 1–2 minutes until the sauce thickens and coats the shrimp.
Remove from heat and serve immediately; garnish with sesame seeds and sliced green onions if desired.