Season the chicken breast evenly on both sides with sea salt, black pepper, and dried oregano.
Heat half of 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 exterior is golden brown and the internal temperature reaches 165°F.
While the chicken cooks, whisk together the remaining olive oil, lemon juice, and Dijon mustard in a small bowl to create the dressing.
In a large bowl, combine the mixed baby greens, sliced cucumber, and halved cherry tomatoes.
Drizzle the dressing over the vegetables and toss gently to coat.
Slice the cooked chicken into strips and place them on top of the salad.
Garnish with sliced avocado and pumpkin seeds before serving.