Preheat oven to 400F and spray a baking dish with oil. Spread out lemon slices on the bottom of the dish, along with tomatoes and garlic. Lay cod filets on top, drizzle with olive oil and season with salt, pepper and mustard and tarragon seasoning.
Transfer to oven to bake for 15-20 minutes, or until fish easy flakes with a fork. Remove from oven and finish with an extra squeeze of lemon and drizzle of the cooking juices. Serve with your favorite carb and veggie sources. Enjoy!