Place the Hatch chiles on a burner over medium-low heat until the skins char and blister; this will happen very quickly. Remove to a bowl, cover with plastic wrap and set aside for 15 minutes to steam.
Heat a 10-inch cast-iron skillet over medium heat and add the canola oil, swirling the pan to coat. Add the scallions and cook until slightly softened, stirring, 1 to 2 minutes.
Meanwhile, peel and seed the chile and then it cut into medium dice. Turn the heat under the skillet to low and add the chiles, cream cheese and some salt and pepper. Cook, stirring often, until the cream cheese is melted. Add the sour cream, 1 1/2 cups of the shredded cheese, and the lime zest. Smooth the top and then sprinkle with the remaining 1/2 cup shredded cheese.
Bake until the cheese is melted and bubbly and just starting to brown, about 15 minutes.
Garnish with the dark green scallions and serve with tortilla chips.