Let the refrigerated puff pastry thaw on the counter until soft and pliable.
Meanwhile, in a small skillet, melt the butter and pour in the lemon juice.
Sauté the minced shallot and minced garlic on medium heat until fragrant.
Add in your frozen or fresh chopped spinach. No need to thaw if frozen!
Pour in the cream cheese, shredded parmesan, dill, salt, and black pepper. Cook until everything is fully combined, stirring well. Remove from heat and set aside.
Season your skinless salmon fillets on all sides with the salt, pepper, and Dijon mustard.
In a small bowl, whisk the egg with a bit of water to create an egg wash.
Preheat the oven to 400°F. Add your baking pan to the oven to heat it as well.