Season the chicken tenders evenly on both sides with half of the sea salt, black pepper, and dried oregano.
Heat half of the olive oil in a medium skillet over medium-high heat until shimmering.
Add the chicken tenders to the skillet and cook for 3 to 4 minutes per side, or until golden brown and the internal temperature reaches 165 degrees Fahrenheit.
While the chicken cooks, dice the cucumber into bite-sized pieces, halve the cherry tomatoes, and thinly slice the red onion.
In a small bowl, whisk together the remaining olive oil, red wine vinegar, and the remaining salt, pepper, and oregano to create the dressing.
Arrange the cucumber, tomatoes, and onion in a large bowl and toss with the prepared vinaigrette.
Slice the warm chicken tenders into strips and place them over the salad, then finish by sprinkling the crumbled feta cheese over the top.