Marinate the flank steak with garlic powder, onion powder, smoked paprika, dried oregano, salt, and pepper. Drizzle olive oil over the steak and let it marinate for 15 minutes.
Preheat the grill or stovetop grill pan over medium-high heat. Grill the marinated steak for 5-7 minutes on each side for medium-rare. Let it rest for 5 minutes before slicing.
Cook quinoa according to package instructions. In a large bowl, combine cooked quinoa, halved cherry tomatoes, diced cucumber, and baby spinach. Toss gently to mix.
Assemble the bowl by placing quinoa and vegetable mixture in a bowl, topping with sliced steak, crumbled feta cheese, and sliced kalamata olives. Squeeze fresh lemon juice over the top and garnish with chopped parsley.