Preheat the oven to 400ºF and line a baking sheet with parchment paper.
Add all of the ingredients for the pesto to a high-speed blender or food processor and blend until smooth. Set aside.
Bring a pot of salted water to a boil and add the couscous. Cook until al dente and then rinse with cold water.
Heat the sun-dried tomato oil in a large skillet over medium/high heat. Add the onion and season with a pinch of salt. Saute for 2-3 minutes.
Add the spinach and sun-dried tomatoes to the skillet and toss. Cook until the spinach has wilted and remove from the heat.
Add the cooked couscous, ½ the pesto, and the spinach mixture to a bowl and toss until coated. Season with salt and pepper and toss again.
Next, slice the salmon. Slice down the center of the salmon about an inch down. From the middle, slice diagonally from the middle to the outside edge. Gently fold back each side to make room for the filling.*
Fill the middle of the salmon with the couscous and gently fold the salmon edges over the filling.
Season the salmon with salt and pepper and place the lemon rounds on the top of the salmon.
Bake for 18-20 minutes or until the salmon is flakey.
While the salmon is baking, add the remaining pesto to a bowl and add 1-2 tablespoons of the sun-dried tomato oil to the pesto to thin it out. Stir and set aside.
Remove the salmon from the oven and top with the remaining pesto, feta, and freshly squeezed lemon.