Cut the vegetable Julienne and keep aside. Deseed the tomatoes and cucumbers before you slice it.
Place a saute pan over medium heat and add oil. Add the veggies, except cucumber and stir until vegetables cook only halfway. Season with salt and pepper. Keep aside to cool.
Once the vegetables cool, add the cucumber and mayonnaise and mix.
Butter one side of the bread, and place it in a pan or panini maker. Add the filling. Place the other bread on top. Cut and serve.
You can also add cheese slices or grated cheese between the bread to make it cheesy.