Prepare the Vinaigrette: In a small bowl, whisk together olive oil, balsamic vinegar, Dijon mustard, garlic powder, and salt until well combined.

Prepare the Mixed Greens: Rinse and dry leafy greens; tear into bite-sized pieces and place in a large mixing bowl.

Chop the Vegetables: Slice cucumber, halve cherry tomatoes, and thinly slice red onion, adding them to the bowl with mixed greens.

Add Olives and Feta: Stir in Kalamata olives and crumbled feta; toss gently to combine.

Dress and Toss the Salad: Drizzle vinaigrette over the salad and toss gently to coat all ingredients.

Serve Beautifully: Transfer to a platter or serving bowl; consider garnishing with additional feta or fresh herbs.