Place the spinach in a strainer and firmly press it down to remove excess water. Spread the spinach over 2 layers of paper towels, then cover with 2 more layers of paper towels and firmly press down to draw out more water from the spinach. Transfer to a large mixing bowl.
Warm the oil in a large skillet set over medium heat. Add the leeks and cook, stirring from time to time, for 8 minutes. Add the garlic and cook for 2 minutes more. Transfer the mixture to the bowl with the spinach, then stir to combine. Let cool for a few minutes.
Preheat the oven to 190 °C (375 °F). Grease a 23-cm (9-in.) round cake pan with removable bottom. Set the pan on a baking sheet.
To the bowl with the spinach and leek mixture, add the eggs, crumbled Saputo Feta Cheese, Saputo Shredded Parmesan Cheese, basil, oregano, dill, and lemon zest. Stir to thoroughly combine the ingredients.
Lay one sheet of phyllo pastry flat on a working surface. Using a pastry brush, lightly butter the whole surface of the pastry. Spread a third of the filling along the bottom of the sheet of phyllo pastry, then roll loosely to create a long cylinder. Repeat to create three cylinders. Transfer one cylinder to the prepared baking pan and gently push it along the edge of the pan. Add the second cylinder, curving it to follow the shape of the first one and rolling it onto itself. Add the last cylinder to finish the spiral. Brush with butter all over, then sprinkle with sesame seeds.
Bake for 25 to 30 minutes, or until the phyllo pastry is deep golden brown and crisp.
Place the pan over a wire rack and let the tart cool completely, about 1 hour, before unmoulding and serving.