Preheat your oven to 400°F and line a baking sheet with parchment paper.
Season the chicken breast evenly with sea salt, black pepper, and dried oregano on both sides.
Roast the chicken for 20 to 25 minutes until the internal temperature reaches 165°F and the exterior is lightly golden.
While the chicken is roasting, chop the cucumber into bite-sized pieces, halve the cherry tomatoes, and thinly slice the red onion.
In a small bowl, whisk together the olive oil and lemon juice until the dressing is well combined.
Allow the roasted chicken to rest for 5 minutes before slicing it into thin strips and dicing the fresh avocado.
Place the mixed greens in a large bowl, toss with the lemon vinaigrette, and top with the sliced chicken, vegetables, avocado, and a sprinkle of hemp seeds.