Sausage, Pepper and Cornbread Skillet Pie

Heat oven to 400 °F. Heat the oil in a large cast-iron skillet over medium heat. Add the sausage and cook, turning, until browned on all sides, 3 to 4 minutes. Transfer the sausages to a cutting board and cut into 1-in. pieces. Add the peppers and onion to the skillet and cook, stirring occasionally, for 4 minutes; stir in the garlic. Add the chard, 1/2 tsp salt and 1/4 tsp pepper, and cook until the chard is beginning to wilt, 1 to 2 minutes. Remove from heat and stir in the sausage. Meanwhile, in a bowl, whisk together the corn muffin mix, Parmesan and 1/4 tsp pepper. Add the milk and egg and mix to combine. Spread the batter over the sausage mixture, leaving a 1/2-in. border. Bake until golden brown and a toothpick inserted into the cornbread comes out clean, 15 to 20 minutes.