Take the one half of the cucumber and shred on a cheese grater. Place the shredded cucumber in a cheese cloth or thin dish towel, and strain the juice out of it.
Place all of the ingredients for the tzatziki, including the pressed cucumber, into a food processor. Process until smooth. Taste to see if you need to add any salt or pepper.
Preheat your oven to 425 degrees Fahrenheit. Brush the flatbread with olive oil, then sprinkle with salt and pepper. Sprinkle with your desired amount of dried rosemary, thyme, and oregano.
Bake the flatbread on the top rack for about 5 minutes, or until the tops become golden and crisp. Let cool slightly and cut into wedges. Serve alongside the tzatziki.