Set oven rack about 6 inches from the heat source and preheat the oven's broiler. Line a baking sheet with aluminum foil and spray with cooking spray.
Melt butter and olive oil together in a skillet over medium-high heat. Saute mushrooms, scallions, and garlic in hot skillet until mushrooms have released their liquid and the liquid evaporates, about 10 minutes. Remove from heat, stir parsley into mushroom mixture, and let mixture cool slightly, about 5 minutes.
Stir mushroom mixture, cream cheese, Parmesan cheese, and Creole seasoning together in a bowl. Stuff each hollowed-out poblano pepper with mushroom mixture and place on prepared baking sheet.
Broil in the preheated oven, turning once, until stuffing is hot and peppers are browned, 8 to 10 minutes.
