Heat olive oil in a pan over medium heat. Cook garlic until fragrant, then add spinach. Cook until wilted. Mix in cream cheese, salt, pepper, and lemon juice, then let cool slightly.

Place salmon fillets on a board and pat dry. Season with salt and pepper. Spread Dijon mustard over each fillet to add flavor and keep fish moist during baking.

Lay puff pastry on a clean surface and lightly roll if needed. Cut into two equal portions so each salmon fillet can be wrapped neatly for even baking and sealing.

Place spinach filling on pastry. Add salmon fillet on top, then more filling if desired. Wrap pastry around salmon tightly and seal edges well so filling does not leak during baking.

Beat egg in a bowl and brush over pastry. Make small slits on top to allow steam to escape. This helps pastry bake evenly and turn golden and crisp in oven.

Place wrapped salmon on baking tray lined with parchment paper. Bake at 400°F for 25 to 30 minutes until pastry is golden brown and salmon is cooked through and tender inside.

Remove from oven and let rest for 5 minutes before slicing. This helps juices settle inside. Serve warm for best flavor, flaky texture, and beautiful presentation at the table.