Heat a medium skillet over medium heat.
Add the beef and cook thoroughly, breaking it up into crumbles with a spoon or spatula as you go. Remove cooked beef from the pan and set aside on a plate or bowl. *Ground Beef should be cooked to an internal temperature of 160F.
If there is a significant amount of grease in the pan, carefully wipe some out with a paper towel. Leave a small amount to saute the vegetables in. Add the garlic to the hot skillet and saute for 1 minute, until fragrant. Add the mushrooms and peppers and cook, stirring frequently for about 3-4 minutes until crisp tender.
Pour in the can of crushed tomatoes and season with the salt and pepper. Stir and bring to a gentle boil. Then reduce heat and simmer sauce for 3-5 minutes.
Meanwhile, heat frozen vegetables according to package directions.
Turn off the heat under the skillet and fold in cooked beef crumbles, basil, and red pepper flakes. Season more if desired.
Layer hot spiralized vegetables into 4 large bowls. Top with a fourth of the tomato beef mixture. Sprinkle each with 2 tablespoons of walnuts and parmesan cheese if using. Enjoy!