Season the chicken breast evenly with the garlic powder, half of the sea salt, and half of the black pepper.
Heat a non-stick skillet over medium-high heat and sear the chicken for 6 to 7 minutes per side until the exterior is golden and the center is fully cooked.
While the chicken is resting, whisk together the extra virgin olive oil, lemon juice, lemon zest, and the remaining salt and pepper in a small bowl to create the vinaigrette.
Dice the cucumber into bite-sized pieces, halve the cherry tomatoes, and thinly slice the avocado.
Slice the rested chicken breast into thin strips against the grain to maintain juiciness.
In a large serving bowl, toss the mixed greens with the lemon vinaigrette until coated, then top with the chicken, cucumber, tomatoes, avocado, and fresh parsley.