Preheat oven to 400 degrees. Cook spaghetti squash until soft. (This can be done in the microwave or the oven) While cooking, boil chicken until cooked through and shred with a fork. Cut squash lengthwise, remove seeds and scrape squash from the skin with a fork. Place half of the spaghetti squash in a 9x13" pan. Top with half the black beans, half the chicken, half the enchilada sauce, half the jalapenos (if desired) and half the cheese. Repeat layering with remaining ingredients. Bake for 30 minutes until bubbly and slightly browned on top. Let sit for 5 minutes before serving. Top with cilantro, if desired.