Preheat oven to 425°F (220°C).
In a pan over medium heat, melt butter. Add the garlic and onions, cooking until translucent. About 5 minutes. Add in the artichokes and cook a few minutes more.
Add the spinach, red chili flakes salt, and pepper, cook until spinach is wilted.
Add the breadcrumbs, cream cheese, parmesan, and dill, stirring until mixture is evenly combined. Remove from heat, add in the lemon zest, taste and adjust seasonings as needed. Set aside and allow to cool.
On a cutting board, lay out the sheet of puff pastry with a little flour. Roll it until it fits the size of your fillet. If you fillet is smaller you can cut the puff pastry down to size. Just make sure to leave enough around the edges to fold and cover the entire salmon.
Pat the salmon dry and make sure there are no pin bones. If it's skin on, remove the skin. Place the salmon in the middle of the pastry and season both sides with salt and pepper.
Make sure the flatter side of the salmon is face up. Place several spoonful's of the spinach mixture on top of the salmon, smoothing it out so that it does not spill over the sides. Fold the edges of the puff pastry over the salmon and spinach, starting with the longer sides and then the shorter ends. Trim any excess pastry from the ends, then fold the ends on top. Flip the puff pastry-wrapped salmon over and transfer to a baking sheet lined with parchment paper.
Brush the beaten egg on the top and sides of the pastry. Score the top of the pastry with a knife, cutting shallow diagonal lines to create a crosshatch pattern.
Brush the top again with the egg wash. Sprinkle with flaky sea salt. Bake for 20-25 minutes, until pastry is golden brown.
Slice, then serve immediately!