Cut spaghetti squash in half. Scoop out seeds. Add 1 cup water to small microwave safe casserole dish. Place squash cut side down in dish. Place paper towel over squash. Microwave on high 10 mins.
Saute ground beef in skillet on medium heat. Remove from pan and set aside.
Add olive oil to skillet. Once heated, add diced veggies and garlic to skillet and saute 5 minutes. Add beef to veggie mix. Add tomato sauce. Season with salt and pepper. Heat on medium until warm, stirring occasionally.
Scoop spaghetti strands out of skin with a fork. Top squash with meat sauce. Add parmesan. Spread a little fresh basil on top.