Preheat the Oven: Preheat your oven to 400°F (200°C). Preheating the oven ensures that the salmon cooks evenly and prevents it from sticking to the pan.

Prepare the Salmon: Line a baking sheet with parchment paper. This makes cleanup much easier and prevents the salmon from sticking to the pan. Place the salmon pieces onto the lined baking sheet, skin-side down (if using skin-on fillets). Arrange the salmon fillets so they are not touching each other. This will allow the hot air to circulate evenly around them.

Butterfly the Salmon: 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; leave the salmon flesh still attached at the very bottom and on either end, creating a pocket or a flap. You’re essentially creating a space to hold the stuffing. This step is easier with longer pieces of salmon.

Season the Salmon: Brush the salmon with 1 Tbsp of olive oil and season with salt and pepper. This helps to enhance the natural flavor of the salmon itself. Don’t be afraid to season generously.

Sauté the Spinach: Heat the remaining 1 Tbsp of olive oil in a large pan over medium heat. Once hot, add the packed spinach, Italian seasoning, paprika, cayenne pepper (if using), salt, and pepper. Sauté for a couple of minutes, until the spinach is wilted. You don’t want to overcook the spinach; just cook it until it wilts down and loses some of its volume.

Combine the Filling Ingredients: Turn off the heat. Add the chopped roasted red peppers, feta cheese, and Parmesan cheese to the pan with the wilted spinach. Stir to combine well, pressing down on the feta to soften (“mush”) it until all the ingredients are evenly distributed and stick together. The residual heat from the spinach will help to soften the feta and make it easier to mash.

Stuff the Salmon: Spoon the spinach-feta mixture into the cut part (the “pocket” or flap) of the salmon. Be generous with the filling, but don’t overstuff the salmon to the point where it won’t close properly. Distribute the filling evenly among the salmon pieces.

Bake the Salmon: Place the stuffed salmon in the preheated oven and bake for about 12-17 minutes, depending on the thickness of your fish and your desired doneness. Salmon is cooked through when it flakes easily with a fork. You can also use a meat thermometer to check the internal temperature; it should reach 145°F (63°C). Start checking for doneness at the 12-minute mark and adjust the cooking time as needed. Thicker fillets will take longer to cook than thinner fillets.

Serve: Remove the stuffed salmon from the oven and serve hot. Garnish with fresh herbs, such as parsley or dill, if desired.