Preheat the oven to 400°F.
In a large skillet over medium heat, cook the ground turkey until browned, about 5-7 minutes.
Add the diced onion and minced garlic, cooking until the onion is translucent, about 3-4 minutes.
Stir in the mixed vegetables, thyme, rosemary, Worcestershire sauce, salt, and pepper. Cook for an additional 5 minutes until the vegetables are tender.
Transfer the turkey mixture to a 9x13 inch baking dish, spreading it evenly.
Top with the prepared mashed potatoes, smoothing them out with a spatula.
If desired, sprinkle shredded cheddar cheese on top.
Bake in the preheated oven for 25-30 minutes, or until the top is golden brown and the filling is bubbly.
Let it cool for 5-10 minutes before serving.