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

In a skillet, heat olive oil over medium heat. Sauté the onion and garlic for about 4-5 minutes until translucent.

Add the chopped spinach and cook for 2-3 minutes until wilted, then remove from heat to cool slightly.

In a mixing bowl, combine the cooled spinach mixture with cream cheese and dill. Season with salt and pepper.

Pat the salmon fillets dry and season lightly with salt and pepper.

Roll out the puff pastry on a floured surface and cut it into four squares.

Place a scoop of the spinach filling in the center of each pastry square, then top with a salmon fillet. Fold and seal the pastry edges.

Score the tops of the pastries with a knife and brush with the beaten egg.

Bake on the prepared sheet for 20-25 minutes until golden brown and the salmon reaches an internal temperature of 145°F (63°C).

Rest the Wellingtons for about 5 minutes before serving with lemon wedges.