Season the chicken breast with sea salt, black pepper, and dried oregano on both sides.
Heat olive oil in a skillet over medium-high heat and sear the chicken for 6-7 minutes per side until fully cooked through.
While the chicken rests, whisk together the extra virgin olive oil, lemon juice, and Dijon mustard in a small bowl to create the dressing.
Slice the cucumber into half-moons, halve the cherry tomatoes, and finely dice the red onion.
In a large bowl, combine the mixed baby greens, cucumber, cherry tomatoes, and red onion.
Slice the rested chicken breast and the avocado into thin strips.
Toss the salad with the lemon dressing, top with the sliced chicken and avocado, and garnish with finely chopped fresh parsley.