Step 1: In a medium bowl or a large zip-top bag, whisk together the olive oil, fresh lemon juice, red wine vinegar, minced garlic, dried oregano, salt, and pepper to create the marinade. Add the chicken breasts, ensuring they are fully coated. Cover or seal and marinate in the refrigerator for at least 30 minutes, or up to 4 hours for best results.

Step 2: While the chicken marinates, rinse the quinoa under cold water in a fine-mesh sieve. In a small saucepan, combine the rinsed quinoa with 2 cups of water and a pinch of salt. Bring to a boil, then reduce heat to low, cover, and simmer for about 15 minutes, or until all the water is absorbed. Remove from heat and let stand, covered, for 5 minutes before fluffing with a fork.

Step 3: To make the tzatziki, grate half of the English cucumber. Place the grated cucumber in a clean kitchen towel and squeeze firmly to remove as much excess water as possible. In a small bowl, combine the squeezed cucumber with the Greek yogurt, chopped fresh dill, a squeeze of lemon juice, and a pinch of salt. Stir well and refrigerate until ready to use. Slice the remaining half of the cucumber and prepare the other vegetables by halving the cherry tomatoes and thinly slicing the red onion.

Step 4: Heat a grill, grill pan, or skillet over medium-high heat with a little olive oil. Remove the chicken from the marinade, letting the excess drip off. Cook the chicken for 6-8 minutes per side, until golden brown and cooked through (internal temperature reaches 165°F or 74°C). Transfer the chicken to a cutting board and let it rest for 5-10 minutes before slicing into strips.

Step 5: To assemble the bowls, divide the cooked quinoa among four bowls. Top with the sliced lemon herb chicken. Arrange the halved cherry tomatoes, sliced cucumber, red onion, and Kalamata olives around the chicken. Finish with a generous dollop of tzatziki and a sprinkle of crumbled feta cheese. Serve immediately.