Pat the chicken breast dry and season both sides evenly with sea salt, black pepper, garlic powder, and dried oregano.
Heat half of the olive oil in a medium skillet over medium-high heat. Add the chicken and cook for 6-7 minutes per side until golden brown and the internal temperature reaches 165°F.
While the chicken cooks, prepare the dressing by whisking the remaining olive oil, lemon juice, and lemon zest in a small bowl.
Dice the cucumber, halve the cherry tomatoes, and thinly slice the red onion.
In a large bowl, toss the mixed greens, cucumber, tomatoes, and red onion with the prepared lemon dressing and fresh chopped parsley.
Once the chicken is cooked, let it rest for 3 minutes before slicing it into strips.
Top the salad with the sliced chicken and the avocado slices to serve.