Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.

In a skillet, warm 1 tablespoon of olive oil over medium heat. Add the chopped onion and minced garlic, sautéing until translucent, about 3-5 minutes.

Stir in the fresh spinach and cook until wilted, about 2-3 minutes. Remove from heat and cool slightly.

In a bowl, combine the spinach mixture with cream cheese and fresh dill. Season with salt and pepper, mixing until well combined.

Dry salmon fillets with paper towels and season generously with salt and pepper.

On a floured surface, roll out the puff pastry to ¼ inch thick and cut into four squares.

Place a quarter of the spinach mixture in the center of each pastry square, followed by a salmon fillet. Fold pastry over to seal, pinching edges.

Score decorative slits on top of each Wellington and brush with beaten egg.

Bake for 20 to 25 minutes or until pastry is golden brown and salmon reaches 145°F (63°C).

Let Wellingtons rest for 5 minutes before serving with lemon wedges on the side.