Dice half of the cucumber and combine in a medium bowl with the tomatoes, red onion, olive oil, 2 tablespoons lemon juice, garlic powder, and half of the oregano. Season with salt and pepper, to taste. Cover and set aside until ready to use.
Prepare the Tzatziki sauce by shredding the remaining cucumber with a box grater. Combine in a medium bowl with Greek yogurt, minced garlic, dill, and the remaining oregano and lemon juice. Season with salt and pepper, to taste. Cover and set aside until ready to use.
Just before serving, spread the hummus into a uniform layer on small serving platter (or in an 8” x 8” casserole dish).
Top the hummus with an even layer of the Tzatziki sauce from Step #2.
Use a slotted spoon to drain excess liquid from the seasoned tomato, red onion, and cucumber mixture from Step #1 before spreading on top of the Tzatziki sauce.
Sprinkle olives, crumbled feta and fresh chopped parsley evenly across the top. Serve with vegetables or pita chips or wedges of pita bread.
For best results, prepare the tomato-cucumber mixture and the Tzatziki sauce the night before to give the flavors a chance to combine. Cover and store in the refrigerator until just before ready to use.