In a small bowl, mix together olive oil, oregano, garlic powder, onion powder, paprika, salt, and pepper. Rub this spice mixture all over the chicken breasts, ensuring an even coating. Let the chicken rest for about 10 minutes at room temperature, or refrigerate for up to 4 hours for deeper flavor.

Heat your grill or a large skillet over medium-high heat. If you're using a skillet, add 1 teaspoon of oil to prevent sticking. Cook the chicken for 6-8 minutes per side, until the internal temperature reaches 165°F and the juices run clear. Once cooked, let it rest for 5 minutes before slicing it into strips.

While the chicken is cooking, prepare the tzatziki sauce. Grate half a cucumber and squeeze out excess water using paper towels (around 2-3 tablespoons). In a medium bowl, mix Greek yogurt, the grated cucumber, minced garlic, lemon juice, and dill. Add salt to taste, and refrigerate for at least 30 minutes to let the flavors meld.

To assemble your Mediterranean Chicken Bowl, divide the cooked quinoa among four bowls. Top each bowl with slices of the grilled chicken, diced cucumber, halved cherry tomatoes, thinly sliced red onion, Kalamata olives, and crumbled feta cheese. Drizzle the bowls with the chilled tzatziki sauce and serve immediately.