Heat the olive oil in a skillet over medium high heat, and season the salmon with salt and pepper to taste.
Sear the salmon on both sides until cooked through. Set aside and keep warm.
Melt the butter in the skillet over medium heat.
Stir in the onions, and saute until softened.
Mix in the tomato paste, basil, garlic and roasted red peppers, and stir to combine. Saute for 1 minute.
Whisk in the heavy whipping cream, and saute until the sauce begins to thicken.
Toss in the spinach, and simmer until wilted.
Stir in the parmesan cheese.
Return the salmon to the skillet, and spoon the sauce over the fillets before serving.
Notes
You want to lower the heat and simmer the sauce gently to prevent the cream from curdling. This keeps the sauce smooth.Let the salmon rest for a few minutes after searing to keep it juicy when added back to the sauceSalmon continues ooking slightly after removing it from the skillet, so avoid overcooking it.The sauce thickens slightly after refrigeration but loosens again when reheated gently. You mayw ant to add a splash of cream though, to loosen it up.