01 - In a mixing bowl, whisk together the olive oil, lemon juice, minced garlic, dried oregano, ground cumin, smoked paprika, salt, and pepper. Add the chicken breasts and turn to coat evenly. Cover and refrigerate for at least 20 minutes, or up to 2 hours for deeper flavor penetration.
02 - Rinse the rice under cold running water until it runs clear. Heat olive oil in a saucepan over medium heat, add the rice, and toast for 1 to 2 minutes, stirring gently. Pour in the water, season with oregano and salt, then bring to a rolling boil. Reduce the heat to low, cover tightly, and simmer for approximately 12 minutes until all liquid is absorbed. Remove from heat and fluff with a fork.
03 - Grate the cucumber and squeeze out excess moisture using a clean towel or fine mesh strainer. In a small bowl, combine the Greek yogurt, drained cucumber, lemon juice, minced garlic, chopped dill or mint, salt, and pepper. Stir until smooth and refrigerate until ready to serve.
04 - Preheat a grill pan or heavy-bottomed skillet over medium-high heat until it begins to smoke lightly. Remove the chicken from the marinade, allowing excess to drip off, and place onto the hot surface. Cook for 6 to 7 minutes per side until golden char marks appear and the internal temperature reaches 165°F. Transfer to a cutting board and let rest for 5 minutes before slicing against the grain.
05 - Spoon a portion of herbed rice into each of four bowls. Arrange a bed of spinach or arugula alongside the rice. Layer sliced grilled chicken over the greens, then scatter cherry tomatoes, diced cucumber, red onion slices, and halved Kalamata olives around the bowl. Finish with crumbled feta cheese and a generous drizzle of tzatziki sauce.
06 - Sprinkle freshly chopped parsley over each bowl and serve immediately while the chicken is still warm.