Add the onion slices to a small bowl and pour in enough cold water to completely cover the onions. Set aside to soak while you prepare the rest of the salad.

In a large mixing bowl, gently stir together the cooked orzo pasta, diced red bell pepper, diced cucumber, halved cherry tomatoes, and sliced black olives.

Add the olive oil, lemon juice, red wine vinegar, minced garlic, dried basil, sea salt, and black pepper to a mason jar. Cover and shake well to combine.

Drain the sliced onion and add them to the pasta mixture. Pour the dressing over the pasta mixture and toss to combine.

Chill in the refrigerator for 30 minutes and top with crumbled feta right before serving.