Season chicken with salt and pepper, then grill or broil chicken until firm to the touch; dice or shred.
Cook quinoa according to package instructions, fluff, then set aside.
Combine yogurt, lime juice, chili powder, cilantro, cumin, salt and pepper in a bowl to make dressing. Mix thoroughly and set aside.
Combine cooked chicken, quinoa, spinach, tomato, avocado and red onion together with the dressing.