Melt ghee in a large skillet over medium heat. Add in spinach, vinegar, chili flakes, garlic, and 1/2 of the sea salt and black pepper. Mix to combine, then cover for 2 minutes. Remove cover, stir ingredients and continue cooking on the stovetop for 3 minutes.
Place salmon fillets in a casserole dish and season with remaining salt and pepper. Divide the cooked spinach between the salmon, covering and shaping over the top of each fillet.
Bake for 15 minutes or until salmon is thoroughly cooked.