Season the chicken breast with half of the sea salt, black pepper, and dried oregano.
Heat a grill pan or cast-iron skillet over medium-high heat and cook the chicken for 6-7 minutes per side until the internal temperature reaches 165°F.
While the chicken is cooking, chop the cucumber into bite-sized pieces and halve the cherry tomatoes.
Thinly slice the red onion and ensure the Kalamata olives are pitted.
In a small mixing bowl, whisk together the extra virgin olive oil, lemon juice, and the remaining salt, pepper, and oregano to create the vinaigrette.
Remove the chicken from the heat and allow it to rest for 3 minutes before slicing into thin strips.
In a large salad bowl, combine the cucumber, tomatoes, and red onion, then toss thoroughly with the prepared vinaigrette.
Top the salad with the sliced chicken, crumbled feta cheese, and whole Kalamata olives before serving.