1. Preheat your oven to 425°F (225°C) to get started.

2. Boil the potatoes in a large pot of salted water until they're tender and easily pierced with a fork.

3. While the potatoes are boiling, melt a pat of butter in a skillet over medium heat and sauté the squash until it's lightly browned.

4. Next, grease an oven-safe dish with a small amount of butter and carefully place the cod fillets inside.

5. In a separate pan, melt a little more butter over medium heat and sauté the thawed spinach for a few minutes, stirring occasionally. Peel and chop the garlic, then add it to the spinach and season with a pinch of salt and a few grinds of pepper. Spoon the spinach mixture evenly over the cod fillets.

6. Arrange the cherry tomatoes on top of the spinach, then pour the heavy cream over the dish. Sprinkle the grated cheese evenly over the top.

7. Place the dish in the preheated oven and bake for about 20 minutes, or until the cod is cooked through and flakes easily with a fork.

8. Remove the dish from the oven and serve the cod hot, accompanied by the boiled potatoes and sautéed squash on the side.