Season the chicken breast evenly on both sides with dried oregano, sea salt, and black pepper.
Heat 0.5 tbsp of olive oil in a skillet over medium-high heat. Place the chicken in the pan and sear for 6-7 minutes per side until the internal temperature reaches 165°F.
While the chicken is cooking, prepare the vegetables by dicing the cucumber, halving the cherry tomatoes, and thinly slicing the red onion.
In a large salad bowl, combine the mixed greens, cucumber, cherry tomatoes, and red onion.
In a small jar or bowl, whisk together the remaining 0.5 tbsp of olive oil and the lemon juice to create a bright vinaigrette.
Once the chicken is finished, let it rest for 3 minutes before slicing it into thin strips.
Top the garden greens with the warm chicken slices, drizzle with the lemon vinaigrette, and finish with a sprinkle of sunflower seeds.