Char and blister poblanos under broiler on high or over the flame on a gas stovetop. Place in a bowl and cover to cool. Peel peppers and cut them lengthwise, remove the seeds. Arrange them on the bottom of a casserole dish.
Warm the potatoes in the microwave to loosen them up a bit if you’re using leftovers. Add garlic, peppers, cumin, cream cheese, half the cheddar and half the pepper jack to the potatoes and mix to combine. Fill the peppers with the potatoes, about 1/2 cup per potato.