Preheat your oven to 400°F (200°C).Arrange the 6 halved bell peppers open-side-up in a 9x13-inch baking dish.Drizzle the insides lightly with olive oil and season with a pinch of salt and pepper. Bake the empty pepper halves for 10-12 minutes.
In a medium bowl, stir together the softened cream cheese, buffalo sauce, Greek yogurt (or sour cream), garlic powder, and half of the green onions until smooth. Fold in the shredded chicken and half of the shredded cheddar cheese.
Divide the buffalo chicken mixture evenly among the 6 pre-baked pepper halves. Top each one generously with the remaining cheddar cheese.
Return the stuffed peppers to the oven and bake for another 15-20 minutes, until the cheese on top is melted, bubbly, and slightly golden.