Heat oil in a medium non-stick frying pan. Add the leeks; sauté until softened, about 8 minutes. Set aside.
Preheat oven to 190°C. Lightly coat a 23 cm glass pie plate with non-stick cooking spray. Combine the leeks, spinach, rice, eggs, 3⁄4 cup parmesan, marjoram, salt and pepper in a medium bowl. Spoon mixture into the prepared pie plate, smooth the top and sprinkle with remaining parmesan.
Bake until firm and browned, about 30 minutes. Serve warm or at room temperature, cut into wedges.