Slice the chicken breast into thin strips and season evenly with the dried oregano and half of the sea salt and black pepper.
Heat a non-stick skillet over medium-high heat and cook the chicken strips for 5 to 7 minutes until golden brown and cooked through.
In a small glass jar, whisk together the extra virgin olive oil, lemon juice, Dijon mustard, and the remaining salt and pepper to create the vinaigrette.
Prepare the vegetables by slicing the cucumber into half-moons, halving the cherry tomatoes, and thinly dicing the red onion.
In a large serving bowl, combine the mixed greens with the prepared cucumber, tomatoes, and onion.
Drizzle the lemon vinaigrette over the salad and toss gently to ensure every leaf is lightly coated.
Top the salad with the warm sautéed chicken and the sliced avocado, then garnish with freshly chopped parsley before serving.