Add garlic, ginger, soy sauce, water, brown sugar, vinegar and sesame oil to a medium saucepan.
Bring to a simmer and cook for 2-3 minutes.
In a small bowl whisk together cornstarch and water.
Slowly whisk in the cornstarch mixture into the saucepan.
Simmer whisking constantly until sauce has thickened up, 1-2 minutes.
Meanwhile, heat olive oil in a large skillet.
Add shrimp and saute until fully cooked.
Add teriyaki sauce to the shrimp and toss to coat.
Serve immediately with green onions and sesame seeds, if desired.
