Mediterranean-Style Pita Pizzas - Forks Over Knives

Ingredients

• ½ cup apple cider vinegar
• 1 tablespoon pure cane sugar
• 1 clove garlic, minced
• 1 large red onion, thinly sliced (1 cup)
• ¾ cup oil-free hummus
• 4 6- to 7-inch whole wheat pita bread rounds, toasted
• 1 10-oz. package heirloom grape tomatoes, halved
• 1 5-oz. package baby mixed salad greens
• 2 tablespoons chopped toasted walnuts