Preheat oven to 400°. Peel and seed butternut squash; cut into 3/4-inch cubes. Toss squash with olive oil to coat; place in a single layer in a lightly greased aluminum foil-lined 15- x 10-inch jelly-roll pan. Bake 20 minutes or until squash is just tender and begins to brown (do not overcook), stirring once after 10 minutes. Cool completely (about 20 minutes).
Toss together cannellini beans, next 4 ingredients, and squash in a large bowl; cover and chill 2 to 4 hours. Toss with arugula just before serving.