Preheat oven to 350°F.
Prepare the Spaghetti squash: Cut squash in half along the longitude line. Scrape out the seeds etc. Place cut side up in baking dish. You want them to sit upright and not tip over, cut the back flat if necessary. Smear insides with crushed garlic,drizzle with oil and salt to taste. Place in preheated oven while going to the next step.
In a skillet, brown the beef with the onion. (optional -- you can add green pepper or other veggies at this step.) Add rinsed quinoa and continue to cook for about a minute then add the beef broth. Bring to a boil before reducing to low. Cover and cook about 15 min until mostly cooked through.When the quinoa is partially cooked but there still is an uncooked spot at the center, remove lid and continue to cook on medium until any extra broth has evaporated.
While the beef/quinoa is cooking, put the tomato paste and diced tomatoes into a sauce pan. Add water and blend with the paste until the consistancy is that of pasta sauce. For me it was about 2/3rd cup. Simmer on the stove with italian spices and salt and other seasonings to your taste. You could also skip this step and substitute your favorite red pasta sauce.This made a scant 3 cups.
Reserve about 1 cup of the pasta sauce and combine the rest with the beef/quinoa. Adjust seasonings to taste.
Remove squash from the oven and fill with the stuffing. Note: You will probably only use half of the stuffing. Put the rest around the squash or you could double the squash to stretch to even more servings.
Top with the reserved pasta sauce and if your diet allows you could add some parmesan cheese.
Cooking time will depend on how cooked the squash got during the preparation time. I kept getting interrupted so mine was in the oven for over an hour. It was almost done cooking so I did not cover the dish but just cooked it long enough for the flavors to blend. When I tried this with raw squash it took well over an hour to cook.
Cooked spaghetti squash is tender when pierced and the flesh shreds easily into "spaghetti" strands. Serve one half squash per person with additional pasta sauce if desired.
I think this could easily be made in the crock pot. I will try it and post the cooking times.