Preheat oven to 400℉
Pat the cleaned hen dry with paper towels. Use 1/2 tsp salt to season the inside of the hen.
Add the garlic, remaining salt, and pepper into a small cup. Carefully lift the skin and add seasoning mixture between the skin and the meat of the hen. Set aside.
Add the orange juice and cornstarch to a small saucepan. Whisk to combine. Add the cranberries, orange zest, and honey.
Bring to a simmer over medium heat and cook for about 5 minutes, or until cranberries start to pop and the glaze thickens. Remove from heat and mash the cranberries with a fork.
Slice the onion into 1/2-inch rings and place them at the bottom of a sprayed oven-safe dish. Season with perfect pinch seasoning. Place the Cornish hen on top of the onions and brush with 1/2 of the glaze.
Place the Cornish hen on top of the onions and brush with 1/2 of the glaze.
Roast in the oven for 25 minutes. Remove and brush with the remaining glaze. Cook for another 25 minutes. If during cooking the hen is nice and brown, cover lightly with foil.
Check for doneness using a meat thermometer. The thighs should register 165 degrees, the breast at 170 degrees.
Serve with the cooked onions.