1Place squash cut-side down in a microwave-safe dish; add 2 tablespoons water. Microwave, uncovered, on High until tender, 10 to 15 minutes.
2Combine spinach and the remaining 1 tablespoon water in a large skillet over medium heat. Cook, stirring occasionally, until wilted, 3 to 5 minutes. Drain and transfer to a large bowl.
3Use a fork to scrape the squash from the shells into the bowl.
4Stir artichoke hearts, cream cheese, 1/4 cup Parmesan, salt and pepper into the squash mixture.
5Divide it between the squash shells and top with the remaining 1/4 cup Parmesan.
6Broil until the cheese is golden brown, about 3 minutes.
7Sprinkle with crushed red pepper and basil, if desired.