1. Bring chicken stock and 1/2 cup water to a simmer in a medium saucepan. Keep warm over low heat. Set aside 1/4 cup of warm stock mixture.
2. Heat a large saucepan over medium heat. Coat pan with cooking spray. Add pancetta; cook 5 minutes or until crisp, stirring frequently. Add mushrooms, onion, and garlic; cook 6 minutes or until tender. Stir in rice and sage; cook 1 minute, stirring frequently. Add wine; cook 30 seconds or until liquid is absorbed. Stir in 1 1/4 cups stock mixture and salt; cook 4 minutes or until liquid is nearly absorbed, stirring constantly. Add remaining stock mixture, 3/4 cup at a time, stirring constantly until each portion of stock is absorbed before adding more (about 22 minutes total). Remove from heat; stir in pumpkin, mascarpone, chives, and pepper. Stir in reserved stock mixture as needed until risotto is desired consistency. Spoon 1 cup risotto into each of 4 bowls; sprinkle evenly with pine nuts.