In a large skillet over medium-low heat, heat the olive oil. Add the onion and leek and cook, stirring occasionally, until very soft, 15 to 20 minutes. Remove from the heat and let cool completely.

Preheat the oven to 350°F (180°C). Oil a 9-by-5-inch (23-by-13-cm) loaf pan and set aside.

Meanwhile, in a large bowl, combine the bread crumbs with the milk. Set aside until the bread crumbs absorb the liquid. Add the lamb, beef, peas, eggs, mint, salt, cumin, paprika, and a few grinds of pepper to the bread crumb mixture and mix gently with your hands to combine. Gently transfer the mixture to the prepared pan (don’t pack it in) and drizzle with a little oil. (You can refrigerate the meatloaf for a few hours before baking; cover well with plastic wrap, and remove it from the refrigerator while the oven heats up.)

Bake until the meatloaf has released some juices and an instant-read thermometer inserted into the center registers 160°F (70°C), 50 minutes to 1 hour. Invert the meatloaf onto a cutting board, turn right side up, and let rest for 10 minutes before slicing and serving.