On a cutting board, start by chopping finely the leeks.
Lightly heat the coconut oil in a frying-pan and add the spices. Mix and add the leeks. Brown them and let them melt for a few minutes over low heat. Then cover the pan and let cook. Add the zest and juice of the 2 limes. Let cook over low heat. When the leeks are tender and melty, turn heat off and set aside.
In a saucepan, blend the oat milk, cornstarch and a pinch of salt and heat up. Keep the mix hot without bringing it to a boil. The milk will thicken little by little and form a béchamel sauce. Set aside.
Line the bottom of a large baking dish with some béchamel, top it with lasagna sheets, add some more béchamel and some leeks on top, then some more lasagna sheets, béchamel, leeks, so on and so forth. Conclude with a layer of béchamel. Copiously sprinkle sesame seeds on top.
Place in hot oven (180°C – 350°F) and bake for about 40 minutes.