Spray a 2-quart casserole with cooking spray or coat evenly with butter. In a large saucepan, heat the oil and butter and sauté the onion until tender but not brown. Stir in the flour until blended. Slowly stir in the stock, whisking well. Cook the mixture over medium heat until the chicken, peas, potatoes, carrots, salt, pepper and hot sauce is heated through. Turn into the prepared dish, spreading evenly.
To prepare the crust, stir together the cornmeal, flour, baking powder, sugar and salt. Stir in milk, egg and oil in a bowl. Do not overmix. Spoon the batter evenly over the filling. Bake until the top is golden brown, or for about 22 to 25 minutes. Cut into wedges to serve.