Heat 1 tablespoon of olive oil in a skillet over medium heat. Add the finely sliced onion and sauté for about 3-4 minutes until translucent.

Introduce 2 minced garlic cloves and stir for another 30 seconds until fragrant.

Stir in 2 cups of thawed and drained spinach and mix with the sautéed onions for about 2-3 minutes until heated through.

Season the mixture with salt and pepper to taste, then blend in ½ cup of sour cream until smooth.

Preheat your oven to 175°C (347°F). Season the salmon fillets with salt and pepper, then sear each side for around 2 minutes in a separate pan.

Grease a baking dish with olive oil. Arrange the seared salmon fillets skin-side down and top each with the creamy spinach mixture.

Sprinkle 1 cup of shredded mozzarella cheese over the spinach and bake for 15-20 minutes until salmon is opaque and flakes easily.

Remove from oven and let rest for 5 minutes before serving.