To make the Salsa: In a large bowl, combine all the ingredients except the avocado in the order listed. Very gently, fold in the avocado, to avoid smashing the delicate ingredients. Cover and refrigerate until chilled.
To make the Dressing: In a small bowl, combine all ingredients and whisk them well. Cover and refrigerate. To serve, gently fold the dressing into the salsa. Season to taste and serve.