Season the chicken breast evenly on both sides with half of the sea salt, black pepper, and dried oregano.
Heat a skillet over medium-high heat with half of the olive oil and sear the chicken for 5-7 minutes per side until the internal temperature reaches 165 degrees Fahrenheit.
While the chicken is cooking, whisk together the remaining olive oil, lemon juice, Dijon mustard, and the remaining herbs and spices in a small bowl to create the vinaigrette.
Prepare the vegetables by slicing the cucumber into rounds, halving the cherry tomatoes, and slicing the avocado into thin wedges.
Place the mixed greens into a large serving bowl and arrange the prepared cucumber, tomatoes, and avocado on top.
Once the chicken is cooked, let it rest for 3 minutes before slicing it into thin strips.
Add the warm chicken strips to the salad, drizzle with the lemon-herb vinaigrette, and toss gently to combine before serving.