In a heavy skillet cook the onion, the carrots, and the garlic in 2 tablespoons of the oil over moderately low heat, stirring, until the carrots are softened and stir in the bell pepper. Drain the beans, and in a bowl combine them with the vegetable mixture, the chicken stock, the remaining 6 tablespoons oil, the parsley, the lemon juice, and salt and pepper to taste. Let the salad stand, covered and chilled. The salad may be made 1 day in advance and kept covered and chilled. Serve the salad at room temperature with the pita wedges.