Preheat your oven to 400°F and line a baking sheet with parchment paper. Place the salmon fillets skin-side down on the baking sheet.
Using a sharp knife, carefully slice down the center of each salmon fillet lengthwise, creating a pocket without cutting all the way through.
Brush the salmon with 1 tablespoon olive oil and season generously with salt and black pepper.
Heat the remaining olive oil in a large skillet over medium heat. Add the spinach, Italian seasoning, paprika, cayenne pepper, salt, and pepper. Cook for 2 to 3 minutes until the spinach wilts.
Remove the skillet from heat and stir in the roasted red peppers, feta cheese, and parmesan cheese. Press the feta gently while stirring until the mixture becomes creamy and well combined.
Spoon the spinach and feta filling into each salmon pocket, dividing the mixture evenly.
Bake the Stuffed Salmon With Spinach & Feta for 12 to 17 minutes depending on the thickness of the salmon and your preferred doneness.
Remove from the oven and serve immediately while hot and flaky.