Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.
Season the chicken breast on both sides with dried oregano, sea salt, and black pepper.
Bake the chicken for 20 to 25 minutes, or until the internal temperature reaches 165°F.
While the chicken cooks, dice the cucumber and halve the cherry tomatoes.
In a small jar or bowl, whisk together the extra virgin olive oil, balsamic vinegar, and dijon mustard until emulsified.
Place the mixed baby greens in a large bowl and toss with the cucumber, tomatoes, and the prepared vinaigrette.
Allow the chicken to rest for 5 minutes before slicing it into thin strips.
Top the dressed salad with the sliced chicken and a sprinkle of sunflower seeds for a satisfying crunch.