Peel squash and cut in half lengthwise. Remove and discard seeds. Cut squash into 1/2- to 3/4-inch cubes (you should have 2 1/2 cups).
In a 5- to 6-quart pan over medium heat, frequently stir onions, ginger, and garlic in butter until onions are very limp, 10 to 15 minutes.
Add rice and stir often until opaque, about 5 minutes. Add curry powder and stir for 30 seconds longer.
Stir in 1/2 teaspoon salt, squash, and broth. Bring to a boil over high heat; reduce heat, cover, and simmer, stirring occasionally, until rice and squash are tender to bite, 16 to 18 minutes. Stir in cilantro and salt to taste. Spoon into a bowl.