Season chicken thighs with salt & pepper. Heat oil in a heavy bottom pan. Brown chicken on all sides. Remove from pan. Drain off fat.
Sauté onion and peppers until tender; about 10 minutes. Add in garlic and sauté for an additional minute. Deglaze pan with red wine, scrapping up any browned bits. Add plum and canned tomatoes with juice, chicken broth, and seasonings.
Reduce heat to low, cover and simmer for 2 - 3 hours.
Preheat oven to 400 degrees. Cut spaghetti squash in half, length-wise. Scoop out seeds. Rub insides with olive oil. Place cut-side down on a baking sheet and bake for 45 minutes or until a fork pierces the skin easily. Scrape flesh into a bowl. Season to taste. Serve with chicken cacciatore and a dusting of parmesan cheese