Greek Spinach Pasta Salad

• 3 cups baby spinach
• 1 pound cooked, rinsed, and cooled rotini pasta
• 1 ½ cups cucumber, cut in half lengthwise and then into ¼-inch pieces
• 1 pint halved cherry tomatoes
• 1 cup pitted and halved kalamata olives, or black olives
• ½ cup thinly sliced red onion, about half an onion
• 6 ounces crumbled Feta cheese

Red Wine Vinaigrette

• ½ cup extra virgin olive oil
• 2 teaspoons minced garlic 
• 1 teaspoon dried oregano
• 1 teaspoon Dijon mustard
• ¼ cup red wine vinegar
• ½ teaspoon salt
• ½ teaspoon ground black pepper