Preheat the oven to 400°F (200°C).
Trim the ends from the zucchini and cut each in half lengthwise.
Use a spoon to scoop out the centers of the zucchini halves to form boats, leaving about a 1/4-inch shell; reserve half of the scooped zucchini pulp for the filling.
In a mixing bowl, beat the cream cheese until smooth, then whisk in the buffalo sauce until combined.
Stir the shredded cooked chicken and reserved zucchini pulp into the buffalo‑cream cheese mixture until evenly mixed.
Place the zucchini boats in a greased baking dish and evenly fill each with the buffalo chicken mixture.
Sprinkle crumbled blue cheese and shredded mozzarella over the filled zucchini boats.
Cover the dish and bake for 30 minutes, then uncover and bake an additional 10 minutes, until the zucchini is tender and the cheese is melted and starting to brown.
Remove from the oven, drizzle with ranch or blue cheese dressing, and sprinkle chopped green onion over the top before serving.