Place a large, deep skillet or Dutch oven over medium-high heat. Add the olive oil and allow it to heat until shimmering. Carefully add the ground turkey to the hot skillet. Break up the meat using a wooden spoon or spatula, stirring occasionally, and cook until the turkey is fully browned and no pink remains, approximately 6 to 8 minutes.

If your ground turkey released a significant amount of fat or liquid, carefully tilt the pan and use a spoon to scoop out and discard any excess liquid, leaving about one tablespoon of fat behind to cook the vegetables.

Add the diced yellow onion to the skillet with the browned turkey. Reduce the heat to medium and cook the onion for 4 to 5 minutes, stirring often, until the onion has softened and turned translucent. Next, add the minced garlic and red pepper flakes (if using) and cook for just 60 seconds more, until fragrant. Be careful not to burn the garlic.

Add the diced zucchini pieces to the skillet. Pour in the drained diced tomatoes. Sprinkle the mixture evenly with the Italian seasoning, dried basil, kosher salt, and black pepper. Stir all of the ingredients well, ensuring the seasonings are evenly distributed throughout the turkey and vegetables.

Cover the skillet with a tight-fitting lid and reduce the heat to low. Allow the mixture to simmer gently for 8 to 10 minutes. This simmering period allows the zucchini to soften slightly and the flavors to fully meld together. If you prefer your zucchini firmer, reduce the cooking time by a few minutes.

Remove the lid and give the skillet a final stir. Taste the mixture and add any additional salt or pepper as needed based on your preference. If the mixture seems too watery, you can remove the lid and increase the heat slightly to medium-low, allowing the liquid to evaporate for 2 to 3 minutes. Serve the Ground Turkey and Zucchini Skillet immediately, garnishing with fresh parsley or a sprinkle of Parmesan cheese, if desired.