Prepare the Vinaigrette:

In a small bowl, whisk together the vinegar, lemon juice, oregano, and garlic. Slowly add the oil in a steady stream, whisking until emulsified. Season to taste with salt and pepper.

Prepare the salad:

In a large salad bowl, toss together the Mediterranean salad blend, tomatoes, red onion, green and red bell peppers, cucumber, and scallions. Add the dressing to taste and gently toss. Sprinkle the olives and Feta cheese over the salad. Serve immediately.