First sauté the onions in a little bit of olive oil just until tender.
Finely chop the apple and cucumber into very small cubes about 1/4 of a inch.
In a small bowl combine the cooked onions, the apple and cucumber and add just about a cap full of olive oil and enough lemon juice to keep the apples fresh looking. Add just a taste of minced fresh garlic.
On the pizza crust, if desired, brush on a bit of olive oil and then add desired amount of sauce. Add the cucumber/ apple mixture and cook in the oven according to the directions for the pizza crust.