Preheat oven to 400 degrees F. Coat a large baking sheet with cooking spray.
Prepare corn muffin mix according to package directions, adding cheese, pimentos and cilantro when you add other ingredients. Arrange poblano pepper halves on prepared baking sheet and fill each pepper with an equal amount of corn muffin mix.
Bake 18 to 20 minutes, until a wooden pick inserted in 1 muffin comes out clean.
Meanwhile, heat oil in a large skillet over medium-high heat. Add onion and fennel and saute 3 to 5 minutes, until soft. Add chicken, peaches and rosemary and bring to a simmer. Cook for 5 minutes, until chicken is heated through and sauce thickens.
Serve chicken with poblano corn muffins on the side.