Heat broiler. Coat both a large baking sheet and a 9 x15 baking dish with cooking spray.
Place poblano on baking sheet and broil 5 inches from heat for 15 to 20 minutes, turning often to char evenly. Transfer to a bowl, cover and let cool 10 minutes.
Meanwhile, heat butter and oil in a large nonstick skillet over medium high heat. Add scallions and garlic; cook 1 to 2 minutes, stirring often, to wilt scallions. Add corn; cook 2 to 3 minutes then add cilantro. Remove from heat and stir in farmer cheese and salt.
Heat oven to 350*F. Carefully remove the loosened chard skin from the poblanos. Cut in half lengthwise; remove core and seeds. Arrange poblano in baking dish in single layer. Fill each with about 1/2 cup corn mixture.
Bake 10 minutes, top with Cheddar cheese and bake 5 minutes to melt cheese.