Brown Arborio rice tends to be chewier than the regular white Arborio, the short-grain rice most commonly used in risottos. It's perfect for this dish.
Bring broth and water to a simmer in a medium saucepan (do not boil). Keep warm over low heat.
Heat oil in a large saucepan over medium-high heat. Add shallots; cook 1 minute or until tender, stirring constantly. Add mushrooms and garlic; cook 3 minutes, stirring constantly. Add wine; cook 1 minute or until liquid has evaporated. Add rice; cook for 1 minute, stirring constantly. Stir in 1 cup broth mixture; cook 6 minutes or until liquid is nearly absorbed, stirring constantly. Add remaining broth, 1/2 cup at a time, stirring constantly until each portion of broth is absorbed before adding the next (about 55 minutes total). Stir in pumpkin during last 15 minutes of cooking time. Stir in cheese and remaining ingredients.