Mash the avocado in a small bowl. Add 2 tablespoons sour cream, lime juice and oil. Stir in tomato, onion and garlic until combined. Refrigerate until ready to serve. Preheat the oven to 425 degrees. Place the cauliflower and garbanzo beans on a baking sheet. Drizzle with 1 tablespoon olive oil and toss with the chili powder, cayenne, salt and pepper. Roast for 15-20 minutes, stir and add bell peppers. Continue to roast for 10-15 minutes until the vegetables are lightly browned. To assemble, top each pita with the avocado mixture and roasted vegetables. Garnish with the remaining sour cream and cilantro.