Preheat oven to 375 degrees. Spray a 14-inch oval casserole dish with cooking spray.
Spiralize the carrot, turnips and potato with the thickest noodle setting of your spiralizer, cutting the spirals into 8-inch lengths.In a small saucepan, simmer the milk, half and half, rosemary, and thyme. In a large nonstick pan, melt the butter and saute the chopped onion and garlic in butter for 5 minutes, add 3/4 tsp salt and pepper. Add the ground turkey and cook on medium-high heat until browned, approximately 10 minutes.
Remove thyme and rosemary leaves from milk and pour milk mixture onto turkey, simmer 3 minutes.
In a large working bowl combine the spitalized turnips, potatoes and carrots along with meat and the milk mixture, combine well. Pour into a casserole dish, top with scallions, and gruyere cheese
Cover with foil and bake 1 hour, uncover and broil on low for 5 minutes, or until golden on top.
I was very happy with the taste of this dish and the ease of preparation. It should be noted that it is not creamy (the moisture from the veggies keeps it moist) and that the cheese is not ooey-gooey. It just kind of melts into the casserole. I will definitely make this again. The turnips and the herbs gave it wonderful flavor. I was out of scallions, but will make sure to add them next time.