In large skillet, heat 1 tbsp (15 mL) of the oil over medium heat; cook onion, stirring often; for 5 minutes or until softened. Stir in rosemary and garlic; cook for 1 minute. Stir in apples and 2 tbsp (25 mL) of the apple cider; cook, stirring occasionally, until apples are softened. Let cool slightly. Stir in goat cheese just until combined.

Slice chicken breasts in half horizontally almost but not all the way through; open like a book. Divide filling among breasts; fold back over and press to seal. Wipe skillet with paper towel. Add remaining oil and heat over medium-high heat; brown chicken lightly on both sides, turning carefully. Remove to plate.

Whisk cornstarch into remaining apple cider. Add to skillet and cook, stirring until thickened slightly. Return chicken to pan; cover and simmer for 6 to 8 minutes, or until chicken is no longer pink inside, basting occasionally with sauce. Season with salt and pepper to taste.