Place sun-dried tomatoes in a bowl and cover with warm water. Soak for 15 minutes. Drain and chop.

Lightly dust cod with flour and season with salt and pepper. Heat butter in a skillet and cook cod until lightly browned, about 3 minutes per side. Transfer cod to a baking dish with a lid.

Preheat the oven to 350 degrees F (175 degrees C).

Add onion to skillet and cook over medium heat until soft and translucent, about 5 minutes. Add drained sun-dried tomatoes, tomatoes, zucchini, creme fraiche, rosemary, salt, and pepper. Cook for 2 minutes. Stir in tomato paste to thicken sauce. Pour mixture over fish in the baking dish and cover.

Bake in preheated oven until fish flakes easily with a fork, about 30 minutes.