Preheat the oven to 400°F (200°C).
Heat a small pan over medium heat with a drizzle of olive oil. Sauté the chopped kale for about 5 minutes, or until softened. Transfer the kale to a bowl. Add the feta cheese, lemon zest, dill, garlic powder, salt, and black pepper. Mix well, using a fork to break up any clumps of feta until the mixture is creamy and well combined.
Using a sharp knife, carefully slice an opening into one side of each salmon fillet, creating a pocket without cutting all the way through.
Spoon the feta mixture into each pocket, filling the salmon evenly. Place the stuffed fillets skin-side down on a parchment-lined baking tray.
Brush the tops of the salmon with a thin layer of Dijon mustard.
In a small bowl, combine the breadcrumbs with a drizzle of olive oil, paprika, garlic powder, dried parsley, and a pinch of salt and pepper. Mix well. Spoon and gently press the breadcrumb mixture over the tops of the salmon fillets.
Bake for 10 to 12 minutes, or until the salmon is cooked through and the topping is golden and crisp.
Finish with a squeeze of fresh lemon juice just before serving.