Meanwhile, to assemble the slaw: In a medium mixing bowl, combine the cabbage, black beans, bell pepper, green onion, cilantro, lime juice, olive oil and salt. Toss to combine and set aside to marinate.
To roast the spaghetti squash: Preheat the oven to 400 degrees Fahrenheit. Place the halved spaghetti squash on a large baking sheet lined with parchment paper and drizzle with 2 tablespoons olive oil. Rub the olive oil all over each of the halves, adding more if necessary. Sprinkle the insides of the squash with freshly ground black pepper and salt. Turn them over so the insides are facing down and roast for 40 to 60 minutes, until the flesh is easily pierced through with a fork.