Roasted Garlic Chickpea Burgers

Name: Roasted Garlic Chickpea Burgers
Ingredients: FOR THE BURGER; ⅓ cup olive oil, separated; 1 small onion, finely chopped; 1 small stalk celery, finely chopped; 1 tbsp. fresh thyme leaves; Salt and pepper, to taste; 1 15oz. can chickpeas, rinsed and drained; 1 cup cooked brown rice; 8 cloves garlic, roasted and peeled; ¼ cup sesame tahini; 2 tsp. lemon zest; ¼ cup finely chopped parsley; 1 egg; FOR SERVING; 2 oz. sprouts; 1 small cucumber, thinly sliced; 2 Roma tomatoes, cored and sliced ½ thick; 3 oz feta, crumbled; 3 pocket pitas cut in half crosswise, or 6 hamburger buns, split and toasted