Preheat oven to 375°.
Cut squash in half lengthwise; discard the seeds and membrane. Place squash halves, cut sides down, on a baking sheet; bake at 375° for 50 minutes or until squash is tender. Cool. Peel squash; mash pulp. Set aside 1 cup pulp, reserving remaining pulp for another use.
Bring water and broth to a simmer in a large saucepan. Keep warm over low heat. Place a Dutch oven coated with cooking spray over medium-high heat until hot. Add radicchio to Dutch oven; sauté 2 minutes or until wilted. Place radicchio in a bowl. Sprinkle with 1/8 teaspoon pepper. Melt butter in Dutch oven. Add onion; sauté 3 minutes or until lightly browned. Add rice; sauté 1 minute. Stir in wine and 1/2 cup broth mixture; cook 3 minutes or until the liquid is nearly absorbed, stirring constantly. Add 2 cups broth mixture, 1/2 cup at a time, stirring constantly until each portion of liquid is absorbed before adding the next (about 15 minutes total). Stir in squash pulp. Repeat procedure with remaining 1 1/4 cups broth mixture (about 9 minutes total). Stir in radicchio mixture and half-and-half. Remove from heat; stir in cheese. Sprinkle with 1/8 teaspoon pepper.