In a large bowl, mix together the breadcrumbs, almonds, and walnuts. Butter an 8- or 10-inch round baking pan.
Place two phyllo sheets vertically in front of you on a work surface. Break apart about a fistful of the kataifi by hand, separating the strands as you would a skein of wool or thread, and strew the strands in the middle of a phyllo pastry, in a line across the phyllo width. Sprinkle a third or a quarter of the nut and breadcrumb mixture – depending on whether you’re using 6 or 8 phyllo sheets – over the kataifi.
Bring up the two sheets of phyllo together and fold them over the kataifi-nut filling joining the edges at the other end of the phyllo, so that you are essentially folding the phyllo in half vertically over the mixture.
Starting from the folded bottom, gently roll the phyllo into a cylinder that’s firm enough to keep the filling securely inside. Trim off the edges of the baklava roll and cut it in small bite- size pieces, about 1 ½ or 2 inches long. Place the pieces inside the buttered pan, snuggly next to each other, starting at the inner rim and working your way around the rim of the pan.
Drizzle at least half the melted butter over the baklava. Bake in a preheated oven for 2 hours at 325F/165C. The baklava needs to bake rather slowly, so that the inside pastry is fully cooked through.
As the baklava bakes, prepare the syrup by simmering all the ingredients together for 8 minutes, until the sugar is completely dissolved and the syrup thickish. Cool the syrup.
When the baklava is ready, remove the cinnamon stick and lemon zest from the cooled syrup and pour it over the hot baklava slowly, allowing it to spread everywhere and be absorbed. Let the baklava rest for at least a half hour before serving.