Season the chicken breast evenly with half of the olive oil, sea salt, black pepper, garlic powder, and dried oregano.
Heat a grill pan or outdoor grill over medium-high heat and cook the chicken for 6-7 minutes per side until the internal temperature reaches 165°F.
While the chicken rests, chop the cucumber into bite-sized pieces, halve the cherry tomatoes, thinly slice the red onion, and dice the avocado.
In a large mixing bowl, whisk together the remaining olive oil and lemon juice to create a bright, emulsified dressing.
Add the mixed baby greens, cucumber, tomatoes, and red onion to the bowl and toss gently until every leaf is coated with the vinaigrette.
Slice the grilled chicken into thin strips and arrange them over the salad, finishing with the diced avocado for a creamy texture.