Preheat the oven to 375°F and line 2 cookie sheets with foil. Cut squash in half lengthwise and scrap out the seeds with a spoon. Rub oil on the ends and place squash face down on cookie sheet. Bake for 30-45 minutes or until done.
Meanwhile, in a large skillet over medium-high heat, saute the red onion, peppers and jalapeno in extra virgin olive oil and cook for 2-3 minutes. Stir in garlic and cook for another minute, stirring occasionally. Add salsa, cumin and salt and pepper to taste and cook to desired doneness.
When the squash is done cooking, allow it to cool for a few minutes before handling. Scrape about 3/4 of the inside into a dish. Place a layer of pepper mixture, black beans and cheese in each squash bowl. Top with the spaghetti squash and another layer of pepper mixture, black beans and cheese.
Broil in the oven for about 5 minutes until the cheese is bubbly and golden brown. Top with green onion, cilantro and avocado slices (or guacamole) and serve immediately.