Prepare the chicken marinade. In a medium bowl, whisk together 30ml (2 tbsp) of olive oil, 15ml (1 tbsp) of lemon juice, 1 tsp dried oregano, 1 tsp garlic powder, 1 tsp salt, and 0.5 tsp black pepper. Add the chicken breasts to the marinade, ensuring they are fully coated. Cover and refrigerate for at least 30 minutes, or up to 4 hours.

Cook the quinoa. Rinse the quinoa thoroughly under cold water. In a medium saucepan, combine the rinsed quinoa with 400ml (1.7 cups) of water or vegetable broth and a pinch of salt. Bring to a boil, then reduce heat to low, cover, and simmer for 15 minutes, or until the liquid is absorbed and the quinoa is tender. Remove from heat and let it steam, covered, for 5 minutes. Fluff with a fork.

Grill or pan-sear the chicken. Heat the remaining 30ml (2 tbsp) of olive oil in a grill pan or skillet over medium-high heat. Remove chicken from marinade and cook for 6-8 minutes per side, or until cooked through and no longer pink in the center. The internal temperature should reach 74°C (165°F). Let the chicken rest for 5-10 minutes before slicing.

Prepare the vegetables. While the chicken is cooking and resting, prepare the vegetables. Dice the cucumber and tomatoes. Thinly slice the red onion. Halve the pitted Kalamata olives.

Make the tzatziki sauce. In a small bowl, combine 200g (0.44 lb) of plain Greek yogurt, 2 tbsp chopped fresh dill, 1 tbsp chopped fresh mint, 1 minced garlic clove, 15ml (1 tbsp) lemon juice, 1 tsp red wine vinegar, and a pinch of salt and pepper. Stir well to combine. If the sauce is too thick, you can add a teaspoon of water or more lemon juice.

Assemble the bowls. Divide the cooked quinoa among four bowls. Slice the rested chicken and arrange it over the quinoa. Add the diced cucumber, tomatoes, sliced red onion, and Kalamata olives to each bowl. Drizzle generously with the prepared tzatziki sauce.