Place a large saucepan over medium heat and add in the olive oil. Add in the beef chunks and cook until browned. Remove from the saucepan and set aside in a bowl.
In the juices left in the pan from the beef, add in the garlic and cook for 30 seconds. Then, add in the red onions and red pepper flakes. Cook for 1 minute and then add in the celery and carrots. Cook for 2 minutes to let the vegetables sweat and then add back in the beef chunks. Add the worcestershire sauce, thyme, and cayenne pepper and stir to combine. Then, season with salt and pepper and add in the beef broth and diced tomatoes. Place the bay leaves on top and cover to bring to a boil.
Once brought to a boil, lower to a simmer and cook for 40 minutes, covered. Then, remove the cover and let simmer uncovered for 35 more minutes or until the stew thickens.
Divide the zucchini noodles into bowls and top evenly with spoonfuls of the stew. Let the stew cook a couple minutes over the zucchini noodles and enjoy, garnished with a bit of fresh parsley!