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 the 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 and set aside.
Reduce heat to medium-low and add 1 tbsp butter to the same pan; when melted, add the diced garlic and cook 1 minute until fragrant.
Add the diced roasted red peppers and cook 2 minutes to warm through.
Add the baby spinach and cook until wilted, stirring to incorporate with the peppers and garlic.
Lower the heat to low and stir in 1/2 cup half & half (or heavy cream), 1/4 cup grated Parmesan, 1/4 tsp red pepper flakes, chopped parsley, and salt and pepper to taste; simmer gently until the sauce is warmed and slightly thickened.
Return the salmon to the pan and spoon the sauce over each fillet to heat through, about 1–2 minutes.
Serve the salmon with sauce spooned over, alongside pasta, rice, or steamed vegetables if desired.