Preheat the Oven: Preheat your oven to 375°F (190°C).
Sauté Vegetables: In a large, oven-safe skillet, heat olive oil over medium heat. Add the diced onion and garlic, cooking until soft and fragrant, about 3-4 minutes.
Add Turkey and Greens: Stir in the shredded turkey and sautéed spinach. Cook for an additional 2-3 minutes to combine the flavors, then remove the skillet from heat.
Prepare the Egg Mixture: In a mixing bowl, whisk together the eggs, milk, salt, pepper, dried thyme, and half of the chopped cranberries until well combined.
Combine Ingredients: Pour the egg mixture into the skillet over the turkey and greens, ensuring it distributes evenly. Gently fold in the crumbled feta and the remaining chopped cranberries.
Cook on the Stovetop: Return the skillet to the medium heat for 2-3 minutes, just until the edges begin to set.
Bake the Frittata: Transfer the skillet to the preheated oven and bake for 15-20 minutes, or until the center is firm and the top is lightly golden.
Serve: Remove from the oven, let cool slightly, and garnish with fresh parsley. Slice into wedges and serve warm or at room temperature.