Pumpkin Walnut Pesto: In food processor; pulse walnuts until ground; add oil, sage, Parmesan cheese, parsley, garlic, salt, pepper and red pepper flakes; pulse until combined. Add pumpkin purée; pulse until combined.
Stuffed Chicken Breasts: Preheat oven to 400°F. Fold Pumpkin Walnut Pesto into goat cheese.
Slice each chicken breast in half lengthwise through center, keeping edge intact to open like a book. Season all over with salt and pepper. Stuff evenly with goat cheese and pesto mixture. Secure with toothpicks.
Heat oil in large ovenproof skillet set over medium-high heat; cook chicken for 3 to 4 minutes per side or until golden brown.
Transfer to oven; bake for 13 to 15 minutes or until chicken is cooked through and instant-read thermometer registers internal temperature of 165°F. Let stand for 10 minutes; remove toothpicks before serving. To serve, slice diagonally.
Using skin-on chicken breasts keeps the chicken moist and tender.
Serve with roasted potatoes and roasted or steamed vegetables.