In a large skillet, heat the olive oil over medium heat. Season the salmon fillets with salt and pepper on both sides.
Once the oil is hot, add the salmon fillets skin-side down. Cook for about 4-5 minutes until the skin is crispy. Carefully flip the fillets and cook for an additional 3-4 minutes until cooked through. Remove the salmon from the skillet and set aside.
In the same skillet, reduce the heat to low and add the butter. Once melted, add the minced garlic and sauté for about 30 seconds until fragrant.
Add the fresh spinach to the skillet and stir until wilted, about 2-3 minutes.
Stir in the lemon juice and season with salt and pepper to taste.
Return the salmon to the skillet, spooning some of the garlic butter sauce over the top. Cook for an additional minute to heat through.
Serve the salmon on a plate with the sautéed spinach and lemon wedges on the side.