For the sauce: Grate cucumbers into a nut milk bag, or on top of a few paper towels, then squeeze the moisture out over the sink. Transfer the cucumbers to a bowl, then add the remaining sauce ingredients and stir to combine; set aside.
Divide the cooked quinoa into 2 bowls, then add the cucumbers, tomatoes, red onion, and feta cheese on top.
Drizzle a few tablespoons of tzatziki over the quinoa and enjoy!
