Preheat oven to 400 degrees F.
To roast the sweet potatoes, brush sweet potatoes lightly with butter on skins and split halves. Arrange potatoes and poblano pepper halves on a rimmed baking sheet.
Bake in preheated oven for 25-30 minutes or until potatoes are cooked through yet still slightly firm, and skins are slightly withered and golden.
Remove from oven and allow potatoes to cool for 10 minutes.
When potatoes are cool enough to handle, lightly score the flesh with a paring knife to create a grid pattern. Gently scoop potato flesh into a large bowl, careful to leave potato skins intact. Place skins, hollowed side up, back on baking sheet.
Dice poblano peppers and add to bowl with potatoes. Add black beans, cumin, chili powder, a 1/4 cup of the cheese and salt and toss gently to combine.
To stuff the potato skins, divide mixture evenly between potatoes skins, top with the remaining 3/4 cup of cheese.
Switch oven to broil and place baking sheet back in the oven. Broil for 2-3 minutes or until cheese is melted and golden.
To make the sauce, combine Greek yogurt, chipotle hot sauce, lime juice and salt in a small bowl and stir until smooth.
Remove potato skins from oven and top with cilantro, onion, diced avocado and yogurt sauce. Serve immediately.