Whisk together all of the other ingredients in a jug (apart from the spring onion garnish) and pour over the chicken breasts. Cook on high for 3-4 hours or on a low setting for 4-5 hours
150 ml Diet Coke, 200 ml BBQ Sauce, 2 tablespoon Tomato Puree, 1 teaspoon Garlic Powder, 1 teaspoon Smoked Paprika, 1 teaspoon Worcestershire Sauce, 1 teaspoon Soy Sauce, ½ teaspoon Light Brown Sugar, ½ teaspoon Salt, ½ teaspoon Black Pepper