In a bowl, toss the cubed chicken breasts with olive oil, lemon juice, minced garlic, dried oregano, salt, and pepper. Let marinate for 15 minutes.

Rinse the quinoa thoroughly. Bring 2 cups of water or broth to a boil in a saucepan, add the quinoa, reduce to a low simmer, cover, and cook for 15 minutes. Remove from heat, let rest for 5 minutes, then fluff with a fork.

Grate the cucumber and squeeze out excess moisture using a paper towel. Mix the dry cucumber into the Greek yogurt along with lemon juice, chopped herbs, and a pinch of salt until smooth and creamy.

Heat a cast-iron skillet over medium-high heat. Add the marinated chicken chunks in a single layer. Sear undisturbed for 3-4 minutes to develop a slight char, then flip and cook for another 3 minutes until cooked through.

Divide the fluffy quinoa among teal ceramic bowls (or your preferred serving dishes). Top with the charred chicken chunks, halved cherry tomatoes, sliced cucumbers, and diced red onions. Add a generous dollop of tzatziki sauce in the center, then garnish with crumbled feta cheese and fresh chopped parsley.