Wash the leek, slice it and let it dry in a pan first with a drizzle of oil and then with a ladle of salted water.
Wash the tomatoes, cut them into slices and toast them on both sides in a hot pan greased with oil. Peel them and keep them aside warm.
Beat the eggs with a pinch of salt, the basil and the leeks. Heat a tablespoon of oil in a pan, cooking the omelette on both sides. Keep it warm. Toast the bread and slice the mozzarella.
Make 4 sandwiches consisting of 3 slices of bread each alternating all the elements. Cut the sandwiches along the diagonals making 4 triangles. Finally, insert each of the triangles obtained with a skewer.