Wash and thoroughly dry the little gem lettuce. Remove any damaged outer leaves and tear into bite-sized pieces.
Prepare the vegetables: halve the cherry tomatoes, dice the cucumber into ½-inch pieces, and slice the red onion as thinly as possible.
Combine the prepared lettuce, tomatoes, cucumber, and red onion in a large salad bowl.
In a small bowl, whisk together the olive oil and lemon juice until emulsified. Season with salt and freshly ground black pepper to taste.
Drizzle about two-thirds of the vinaigrette over the salad ingredients and gently toss until evenly coated.
Taste and add more dressing if needed.
Top with crumbled feta cheese and any optional add-ins you're using (avocado, toasted pine nuts, or fresh herbs).
Serve immediately for best texture and flavor.
