Marinate chicken: Mix chicken, olive oil, lemon juice, oregano, salt, and pepper in a bowl. Let it sit for 30 minutes.
Cook quinoa: Rinse and cook according to package directions.
Grill or bake chicken: Grill over medium heat or bake in a 400°F oven until cooked. Cool slightly, then slice.
Prep veggies: Dice cucumber, halve tomatoes, and slice onion.
Make yogurt sauce: Combine Greek yogurt, lemon juice, dill, salt, and pepper in a bowl.
Assemble bowls: Divide quinoa, chicken, veggies, and olives among containers. Add feta. Keep yogurt sauce separate until serving.
