01 - In a mixing bowl, whisk together olive oil, lemon juice, garlic, oregano, cumin, smoked paprika, salt, and pepper. Add the chicken breasts and coat thoroughly. Cover and refrigerate for at least 20 minutes, or up to 2 hours for deeper flavor penetration.
02 - Rinse rice under cold running water until the water runs clear. Heat olive oil in a saucepan over medium heat, add the rice, and toast lightly for 1 minute. Pour in the water, season with oregano and salt, then bring to a boil. Reduce heat to low, cover tightly, and simmer for approximately 12 minutes until liquid is fully absorbed. Fluff gently with a fork.
03 - Combine Greek yogurt, grated and thoroughly drained cucumber, lemon juice, minced garlic, chopped dill or mint, salt, and pepper in a small bowl. Stir until evenly incorporated, then refrigerate until ready to serve to allow the flavors to meld.
04 - Preheat a grill pan or skillet over medium-high heat. Remove chicken from the marinade and cook for 6 to 7 minutes per side, or until the internal temperature reaches 165°F and the juices run clear. Transfer to a cutting board and let rest for 5 minutes before slicing against the grain.
05 - Divide the herbed rice evenly among 4 bowls. Arrange a bed of spinach or arugula alongside the rice in each bowl. Layer with sliced grilled chicken, halved cherry tomatoes, diced cucumber, red onion slices, Kalamata olives, and crumbled feta cheese. Drizzle generously with tzatziki sauce.
06 - Finish each bowl with a sprinkle of freshly chopped parsley. Serve immediately while the chicken is still warm.