Start by cutting the salmon into 2 fillets and making sure there are no bones or scale in the skin. You can remove the scale with a knife by working against the direction of the scales. Rinse the fish under water when done.
Season the salmon fillets with salt and black pepper to taste.
In a medium heat pan, add the oil and the butter. Once the butter is melted, add the salmon skin down. Cook for about 3 minutes.
Turn the salmon and cook for another 3 minutes. To be sure the salmon is fully cooked, you can measure the internal temperature with a thermometer. It should be 145°F (63°C). Remove from the pan and reserve.
Add the onions. Stir fry it for about 2 minutes. Add the garlic and stir fry it for about 1 minute.
Add the cooking cream, salt and black pepper. Mix it well.
Add the spinach and the parmesan. Cook for about 4 minutes. Finally, add the lemon juice, mix it well and remove it from the heat.
Place the salmon back to the skillet and add sliced lemon to serve. Enjoy it with a side of pasta, mashed potatoes, salad or rice.