Pat the salmon fillets dry and season both sides with salt and pepper.
Heat 1 tbsp olive oil in a medium non-stick skillet over medium heat.
Place salmon in the skillet flesh-side down and cook about 5 minutes, then flip and cook another 5 minutes, or until cooked to your liking; remove salmon from the pan and set aside.
Reduce heat to medium-low and add 1 tbsp butter to the same pan; add the diced garlic and cook 1 minute until fragrant.
Add the diced roasted red peppers and cook 2 minutes, stirring to combine.
Add the fresh spinach and cook until wilted, about 1–2 minutes.
Reduce heat to low, then stir in 1/2 cup Half & Half or heavy cream, 1/4 cup grated Parmesan, 1/4 tsp red pepper flakes, and chopped parsley; season with salt and pepper and bring to a gentle simmer.
Return the salmon to the pan and spoon the sauce over each fillet to heat through, about 1–2 minutes.
Serve the salmon with the roasted pepper sauce over pasta, rice, or steamed vegetables.