Season the chicken breast evenly on both sides with sea salt, black pepper, and dried oregano.
Heat a non-stick skillet over medium-high heat and sear the chicken for 6 to 7 minutes per side until the exterior is golden and the internal temperature reaches 165 degrees Fahrenheit.
While the chicken cooks, dice the cucumber into small cubes, halve the cherry tomatoes, and finely mince the red onion.
In a small glass jar or bowl, whisk together the olive oil and lemon juice until well combined to create the dressing.
Transfer the cooked chicken to a cutting board and let it rest for 3 minutes before slicing into thin strips.
In a large mixing bowl, combine the arugula, cooked quinoa, cucumber, tomatoes, and red onion.
Drizzle the dressing over the salad and toss gently to coat all ingredients.
Top the salad with the sliced chicken and a sprinkle of chopped fresh parsley before serving.