Using a large, sharp knife, pierce a spaghetti squash in several places.Place the spaghetti squash in a glass baking dish and cook in the microwave on high for about 15 minutes, turning the squash halfway through cooking.
Before handling, let the squash stand for 10 minutes. Cut it in half lengthwise and scrape out the seeds and fibers.
Using a fork, twist out strands of the spaghetti squash flesh and place in a large bowl. Let stand at room temperature. Save the shells of the squash for stuffing later.
Preheat the broiler.
Heat the olive oil in a large nonstick skillet set over medium heat. Add the onion and cook until tender, about 5 minutes. Add the red bell pepper and cook until just tender, about 2 minutes. Add the garlic and cumin, and cook for 30 seconds.
Stir in the spaghetti squash strands, black beans, corn and enchilada sauce, and cook until heated through, about 2 minutes. Season with salt and pepper.
Scoop the spaghetti squash mixture into the spaghetti squash shells and top with the Monterey Jack cheese.
Place the stuffed spaghetti squash onto a baking sheet and place under the broiler. Cook until the cheese is melted, about 2 minutes.