We suggest you serve this with a grating of Pecorino Cheese and a simple salad with vinaigrette dressing. And wine, obviously. And bread for mopping if you like gluten.
For spaghetti: Preheat Oven to 375. Rub insides of each half of the spaghetti squash with 1-2 Tbls olive oil, and season with salt and pepper. Place squash cut-side down on a parchment-lined sheet tray and bake for 40 minutes, rotating tray halfway through baking. Remove from the oven and let sit for 20 minutes. Flip squash over, and using a fork, shred the meat of the squash away from the skin into spaghetti-like strands, working from the sides of the squash into the middle. Scrape back onto the sheet tray, drizzle with 1 T olive oil, season with salt, pepper and marjoram.
While you roast the squash, prepare The Sauce.
In a large sauce pot over high heat, heat 1 Tbls olive oil. Add pork, season with salt and pepper, and sauté 5-7 minutes until browned. Remove from pot and set aside. Melt 1 Tbls butter and 1 Tbls olive oil in the pot. Add the mushrooms, season with salt and pepper and sauté 5-7 minutes until browned. Remove and set aside. Add 1 Tbls butter and 1 Tbls olive oil to the pot, and add onions, carrots, celery, and bell peppers. Season with salt and pepper and sauté until just starting to brown—about 5-7 minutes. Add the minced garlic and chili flakes, and cook until fragrant, about 30 seconds. Add tomato paste and continue to brown the vegetables for about 2 minutes. Add pork and mushrooms back to the pan. Add herbs, and cook about 2 minutes. Deglaze the pot with the red wine, scraping and stirring the brown bits off the bottom, and cook down for about 2 minutes. Add crushed tomatoes and water, and season with salt and pepper. Bring to a simmer and cook, uncovered, for about 20 minutes over low heat.