Season the chicken breast with salt and black pepper, then grill for 5–7 minutes per side until fully cooked. Let it rest before slicing.
Wash the salad greens, halve the cherry tomatoes, dice the cucumber, and slice the avocado.
Arrange the mixed greens in a large serving bowl.
Top with the grilled chicken, avocado, cherry tomatoes, and cucumber.
Whisk together the olive oil and fresh lemon juice to make a simple dressing.
Drizzle the dressing evenly over the salad.
Serve immediately, garnished with freshly ground black pepper or chopped parsley if desired.