To make Roasted Grapes: Heat oven to 350° F.
In bowl, combine grapes, olive oil, salt, pepper and cinnamon stick.
Lightly spray baking sheet with nonstick cooking spray. Pour grape mixture onto baking sheet. Bake 15 minutes. Remove from oven and pour into bowl.
To make Gastrique: In small saucepan, combine water and sugar. Bring to boil over medium-high heat, 5-7 minutes, until sugar starts to brown.
Remove from heat and slowly add vinegar. Return to heat and stir until combined. Add cornstarch and water mixture; bring to boil. Remove from heat.
Pour Gastrique mixture over Roasted Grapes.