Season the chicken breast evenly with sea salt, black pepper, and dried oregano on both sides.
Heat a non-stick skillet over medium heat with a small portion of the olive oil and sear the chicken for 6 to 7 minutes per side until the internal temperature reaches 165°F.
While the chicken is cooking, prepare the vinaigrette by whisking together the remaining olive oil, balsamic vinegar, and Dijon mustard in a small glass jar or bowl.
Wash and dry the mixed baby greens, then place them in a large serving bowl.
Slice the cucumber into half-moons, halve the cherry tomatoes, and thinly slice the red onion.
Toss the vegetables with the mixed greens until well combined.
Remove the chicken from the pan and let it rest for 3 minutes before slicing into thin strips.
Top the salad with the sliced chicken, drizzle with the balsamic vinaigrette, and garnish with hemp hearts for added texture.