Preheat the oven to 190 ℃ (375 ℉)
Divide the meatball mixture into 8 equal portions and roll each into a ball.
Flatten slightly then use your thumb to press a hollow into the center, forming a cup. Place them in a baking dish, making sure they don't touch each other.
Fill the holes with 1 ½ tablespoons of peas and then top with mashed potatoes using a spoon or a piping bag.
Bake the meatballs for 20 minutes.
Prepare the tomato sauce while the meatballs are baking by mixing tomato paste, water, and thyme in a jug.
Reduce the heat to 180°C (350°F), remove the meatballs from the oven, and top them with grated Kasar cheese.
Pour the tomato sauce around the köfte in the baking dish, making sure not to cover the mashed potato tops.
Return the meatballs to the oven and bake for another 20 minutes, until the cheese has melted and has slightly golden edges.