Toss frozen fries with rosemary. Bake on parchment paper-lined baking sheet according to package directions.
Meanwhile, in a medium saucepan, whisk 1 tbsp (15 mL) broth with cornstarch until smooth, then whisk in remaining broth. Bring to boil over medium-high heat; immediately reduce to a simmer. Cook, whisking frequently, until gravy thickens to desired consistency, 1 to 2 min. Remove from heat.
Divide hot fries onto 4 plates. Top with chicken, cheese and hot gravy. Serve immediately.