Preheat oven to 375˚F. Peel squash, then halve lengthwise and scoop out seeds. Roughly chop squash into 3/4" cubes. Oil a baking sheet, and spread the squash out in a single layer. Sprinkle with salt and black pepper to taste. Roast in the oven until tender, about 30 to 40 minutes, turning them over halfway through the cooking time. Set aside to cool slightly. While squash is in the oven, cook farro in a large pot of simmering salted water until the grains are tender but chewy, about 30 minutes. Drain and set aside. In a small bowl, whisk together sherry vinegar, water, 1/2 teaspoon salt and sugar until sugar and salt dissolve. Stir in onion, then cover and refrigerate at least 30 minutes. In a large bowl, toss together butternut squash, farro, red onion and vinegar brine, the crumbled cheese and pepitas. Toss with 3 tablespoons of the remaining olive oil, use the 4th one only if needed. Taste and adjust seasonings. Serve. The salad will keep, covered and refrigerated, for a week.