If using ground turkey, cook the turkey. Heat a medium skillet over medium heat and add 2 tbsp oil. When the oil is heated, add the ground turkey and a pinch of salt and pepper. Cook, breaking up the meat as you go, until it’s cooked through, about 7 minutes. Remove from the pan and set aside. Add the remaining 2 tbsp oil to the pan. Add the celery, carrot, onion, potatoes, herbs, and a pinch of salt and pepper. Saute, stirring occasionally, until the potatoes are almost tender, about 7-10 minutes.
Stir in the flour and let cook for a couple minutes. Slowly stir in the chicken broth and let simmer for another couple minutes. Add the turkey to the pan along with the green peas and stir to combine.
Pour the turkey mixture into a medium baking dish in an even layer.
Make the stuffing: Add the butter to a medium skillet. When the butter melts, add the celery and onion. Saute until mostly tender, about 5 minutes. Stir in the garlic, herbs, and salt and pepper and cook for another couple of minutes.
Spread the stuffing over the turkey mixture in the baking dish. Cover and refrigerate for up to 24 hours to cook later if desired.
If cooking from the refrigerator, bake at 350 degrees fahrenheit for 45-60 minutes or until the bread is golden brown in some places and the edges are bubbling slightly.
If cooking immediately, bake at 350 degrees fahrenheit for 25-30 minutes or until the bread is golden brown in some places and the edges are bubbling slightly.
Let cool for 5-10 minutes before serving.