Pat the chicken breast dry and season both sides with sea salt, black pepper, and half of the fresh oregano.
Heat one teaspoon of olive oil in a medium skillet over medium-high heat.
Add the chicken to the skillet and sear for 6 to 7 minutes per side, or until the internal temperature reaches 165°F and the exterior is golden brown.
While the chicken cooks, whisk together the remaining teaspoon of olive oil, lemon juice, lemon zest, minced garlic, and the remaining oregano in a small bowl to create the dressing.
Slice the cooked chicken into thin strips once it has rested for 3 minutes.
In a large serving bowl, layer the cooked quinoa and fresh spinach, then top with the sliced chicken, halved cherry tomatoes, and diced cucumber.
Drizzle the lemon-herb dressing over the entire bowl and toss gently before serving.