Preheat oven to 400 degrees F. Line a baking sheet with parchment paper.
Top tortilla with spinach, sun dried tomatoes, olives and cheeses, and then top with another tortilla. Repeat with remaining tortillas to make 4 quesadillas.
Place quesadillas onto the prepared baking sheet. Place into oven and bake until the cheese has melted, about 8-10 minutes.
Serve immediately with tzatziki sauce, garnished with dill, if desired.
For the tzatziki sauce
To make the tzatziki sauce, combine Greek yogurt, cucumber, garlic, dill, lemon juice, lemon zest and mint in a small bowl; season with salt and pepper, to taste. Drizzle with olive oil. Refrigerate for at least 10 minutes, allowing the flavors to meld.