Finely slice all the vegetables. Melt the butter in a skillet and lightly cook the vegetables (approximately 1 minute) until soft. Add a pinch of oregano, salt and pepper and mix well. Remove from heat and allow to cool.
Spread the tomato sauce over the pita breads. On the first half of each, spread the ham slices, the vegetables and the Mozzarella slices. Fold the other half across and hold in place with a toothpick.
Serve cold or warm.