Season the chicken breast evenly with half of the sea salt, black pepper, and dried oregano.
Heat a grill pan or 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 rests, finely dice the English cucumber and red onion, and halve the cherry tomatoes.
In a small bowl, whisk together the extra virgin olive oil, lemon juice, remaining oregano, salt, and pepper to create the vinaigrette.
Slice the rested chicken into bite-sized cubes.
In a large mixing bowl, combine the diced cucumber, tomatoes, onion, chicken cubes, and crumbled feta cheese.
Drizzle the vinaigrette over the salad, sprinkle with fresh chopped parsley, and toss gently to combine before serving.