Preheat your oven to 400°F.
In a medium bowl, whisk together the coconut milk, red curry paste, fish sauce, lime juice, garlic, ginger, and brown sugar until well combined.
Place the cod fillets in a baking dish and season with salt and pepper.
Pour the coconut curry mixture over the cod, ensuring the fillets are well coated.
Scatter the cherry tomatoes around the cod in the baking dish.
Bake in the preheated oven for 15-20 minutes, or until the cod flakes easily with a fork.
In the last 5 minutes of baking, add the spinach leaves to the dish, allowing them to wilt in the sauce.
Remove from the oven and garnish with fresh cilantro before serving.