Preheat the oven to 400 degrees F. Scrub the sweet potatoes and dry well; transfer to a baking sheet. Bake until easily pierced with a knife, about 40 minutes. Remove from the oven and let cool 5 minutes.
Roast the poblanos over the flame of a gas burner (or under the broiler), turning, until charred all over, 4 to 5 minutes. Transfer to a bowl, cover with plastic wrap and let cool. Peel off the charred skins and remove the stems and seeds. Finely chop the peppers and set aside.
One at a time, hold each sweet potato with a kitchen towel and halve lengthwise. Scoop the flesh into a large bowl, leaving a 1/4-inch-thick shell. Mash the flesh with the butter, 3 tablespoons crema, the lime zest and adobo sauce until smooth. Stir in the poblanos and scallions; season with salt and pepper. Brush the potato skins with melted butter and season the insides with salt and pepper. Return to the baking sheet.
Mound the filling into the sweet potato skins and sprinkle the tops with the cheese. Return to the oven and bake until the filling starts browning and the skins are crisp, 16 to 18 minutes. Season with salt.
Stir the remaining 3 tablespoons crema in a small bowl with enough lime juice until thin enough to drizzle. Season with salt. Drizzle the lime crema over the sweet potatoes and top with cilantro.