Season salmon fillet with salt, garlic powder and onion powder. Divide 1/2 the spinach between 2 sheets of puff pastry and mound in the center. Place salmon on top of spinach. Spread pesto over salmon and top with remaining spinach. Moisten edges of puff pastry with water (or can use an egg wash), fold to center and seal the seams.
Bake for 20-25 minutes until the pastry is puffed and golden.