Thaw (if frozen) and rinse cooked shrimp. Pat dry with paper towels.
In a 1-quart resealable bag, add honey, soy sauce, garlic, ginger, onion, oil, and red pepper flakes. Mix to combine and set aside half of the marinade. Place the cooked shrimp in the bag, seal it, and refrigerate for 15 minutes.
While shrimps are marinating, place the reserved marinade in a small saucepan. Add 1 tsp of cornstarch and whisk until combined. Heat over medium heat until thickened. This will be the glaze you will use on the shrimp when grilling. Remove from heat and place in a small bowl.
Prepare your grill with oil to prevent the shrimp from sticking. Heat the grill to 350℉.
Remove the shrimp from the marinade and discard it. Add 3 shrimp per skewer. You should have 4 shrimp skewers.
Place shrimp on a hot grill and cook for 30 seconds. Flip over and brush with half of the glaze. Cook for 30 seconds. Flip and add the remaining glaze. Cook for 30 seconds or until shrimp skewers are hot. Serve immediately.