Meanwhile, stir together salsa, broth, and cornstarch in a medium saucepan. Bring to a boil over medium-high. Reduce heat to medium to maintain a simmer. Cook, stirring often, until thickened, about 2 minutes. Spread 1/3 cup of the sauce in the bottom of an 11x7-in. baking dish coated with nonstick cooking spray. Set aside.