Prepare the Cod: Start by preheating your oven to 375°F (190°C). Place the cod fillets in a baking dish, season with salt and pepper, and bake for about 15-20 minutes, or until the fish is cooked through and flakes easily with a fork. Remove from the oven and allow to cool slightly before flaking the fish into large pieces.
Sauté the Vegetables: In a skillet over medium heat, add a drizzle of olive oil. Once hot, add the chopped onion and cook for 3-4 minutes until translucent. Add the minced garlic and chopped spinach, cooking until the spinach wilts, about 2-3 minutes. Remove from heat and let cool.
Mix the Ingredients: In a large bowl, combine the flaked cod, sautéed vegetables, breadcrumbs, shredded cheese, eggs, and lemon juice. Season with salt and pepper to taste. Mix thoroughly until all ingredients are well incorporated.
Form the Cakes: With damp hands, take a portion of the mixture and shape it into a patty. Repeat until all mixture is used up, placing the formed cakes on a plate.
Cook the Cakes: In a large skillet, heat olive oil over medium-high heat. Once hot, add the cakes in batches (do not overcrowd the pan). Cook for 3-4 minutes on each side until golden brown and crispy. Remove from the skillet and drain on paper towels.
Serve: These cheesy cod and spinach cakes can be enjoyed immediately. Serve them warm with a side of tartar sauce or a squeeze of fresh lemon juice.