Season the chicken breast evenly with the sea salt, black pepper, and dried oregano on both sides.
Heat the olive oil in a medium skillet over medium-high heat.
Place the chicken in the skillet and cook for 6 to 7 minutes per side, or until the internal temperature reaches 165°F and the outside is golden brown.
While the chicken is cooking, halve the cherry tomatoes and dice the cucumber into bite-sized pieces.
Mince the garlic clove and whisk it together with the lemon juice in a small bowl to create a simple dressing.
Remove the chicken from the pan and let it rest for 3 minutes before slicing it into thin strips.
In a serving bowl, layer the baby spinach and cooked quinoa as the base.
Arrange the sliced chicken, cherry tomatoes, and cucumber on top of the quinoa.
Drizzle the lemon-garlic dressing over the entire bowl and serve immediately.