Step 1: Cook the Quinoa. Combine rinsed quinoa and vegetable broth (or water) in a medium saucepan. Bring to a boil, then reduce heat to low, cover, and simmer for 15 minutes, or until all liquid is absorbed. Fluff with a fork and set aside.
Step 2: Prepare the Chicken. Pat chicken breasts dry. Rub with 1 tbsp olive oil, oregano, garlic powder, salt, and pepper. Grill or pan-sear chicken over medium-high heat for 6-8 minutes per side, or until cooked through (internal temperature 165°F/74°C). Let rest for 5 minutes, then slice or dice.
Step 3: Make the Dressing. In a small bowl, whisk together extra virgin olive oil, lemon juice, red wine vinegar, Dijon mustard, minced garlic, oregano, salt, and pepper until well combined.
Step 4: Assemble the Bowls. Divide the cooked quinoa among 4 serving bowls. Arrange sliced chicken, diced cucumber, cherry tomatoes, red onion, bell pepper, and Kalamata olives over the quinoa.
Step 5: Garnish and Serve. Drizzle generously with the lemon-herb dressing. Top with fresh parsley, crumbled feta, and diced avocado (if using). Serve immediately.