For the lamb mixture
Heat the olive oil in a skillet. Add the onion and garlic and cook for a few minutes, until soft. Add the minced meat and cook for 5-6 minutes until browned.
Add the remaining ingredients, stir well and let cook for 5 minutes until all fluids are absorbed. Remove the lamb from the heat and set aside.
For the sauce
Place the peppers and garlic in a preheated oven at 200°C for 20 minutes until their skin is blackened and starts to separate from the flesh. Remove the peppers from the oven. Place them in a bowl and cover with cling wrap. Allow the peppers to rest for 15 minutes. Remove the peppers from the bowl and peel.
Peel the garlic cloves and finely chop along with the roasted peppers and place them in a bowl. Add the remaining ingredients and mix well.
For the pie crust
Place the dough in a rectangular baking sheet lined with parchment paper. Spread the sauce on the dough leaving a 1½ cm border from the edge. Sprinkle the pie with grated Gruyère cheese followed by the lamb mixture and topped with the crumbled feta cheese. Fold the edges of the dough to create the pie crust. Brush the crust with the egg and olive oil mixed together and sprinkle the pie with white and black sesame seeds. Cover the pie with foil and bake in preheated oven at 170°C for 20 to 25 minutes; remove the foil for the last 5 minutes.