Preheat oven to 400F. Line a baking sheet with parchment paper. Place salmon pieces onto lined baking sheet, skin-side down.

Using a sharp knife, slice down the middle of each piece of salmon, lengthwise. Make sure that your knife doesn't go all the way through, leaving the salmon flesh still attached at the very bottom and on either end.

Brush salmon with 1 tablespoon of olive oil and season with salt and pepper. Set aside.

Heat remaining 1 tablespoon of olive oil on a large pan, over medium. Once hot, add spinach, Italian seasoning, paprika, cayenne, salt, and pepper. Sauté for a couple minutes, until wilted.

Turn off the heat, then add in chopped roasted red peppers, feta cheese, and parmesan. Stir to combine well, pressing down on the feta to soften ('mush') it, until all ingredients stick together.

Spoon the spinach-feta mixture into the cut part of the salmon. Repeat until all mixture is used up and pieces of salmon are evenly filled.

Place salmon in the oven and bake for about 12-17 minutes, depending on desired doneness and how thick your fish is. Remove from oven and serve hot!