In a large pan, heat the olive oil over medium-high heat. Add the chopped onion and cook until soft and translucent, about 5 minutes. Add the minced meat and cook until browned, breaking it up with a spoon.
Stir in the cinnamon, cumin, salt, and pepper. Cook for another minute until fragrant. Remove from heat and let it cool slightly.
In a bowl, combine the mashed potatoes, cooked minced meat mixture, chopped hard-boiled eggs, and fresh parsley. Mix everything well to create a cohesive filling.
Lay a sheet of 'dyoul' or 'brick' pastry on a clean, flat surface. Place a spoonful of the filling mixture on one end of the sheet.
Fold the sides of the pastry inward to cover the filling, then roll it tightly from one end to the other, creating a spring roll-like shape. Repeat with the remaining pastry sheets and filling.
In a deep pot or large frying pan, heat enough oil for deep-frying to about 180°C (350°F).
Carefully place a few bourek pastries into the hot oil. Fry for 2-3 minutes on each side, or until they are golden brown and crispy. Do not overcrowd the pan.
Remove the bourek with a slotted spoon and place them on a plate lined with paper towels to drain excess oil. Serve immediately while hot, with a fresh squeeze of lemon juice.