Preheat the oven to 425 degrees . Season the chicken with salt and pepper. In a large, ovenproof skillet, heat 2 tablespoons shortening over medium-high heat. Add the chicken and cook, stirring, until browned, about 5 minutes. Add the onion and garlic and cook, stirring, until softened, about 5 minutes. Stir in 2 tablespoons flour and cook, stirring, for 2 minutes. Add the broth and bring to a boil, scraping up any browned bits. Stir in the peas and carrots, lemon peel and lemon juice.
In a bowl, combine the remaining 2 cups flour, the baking powder and 1/2 teaspoon salt. Using your fingertips, rub the remaining 1/2 cup shortening into the dry ingredients. Stir in 1 cup buttermilk to form a dough. Transfer to a floured surface and roll out 1/2 inch thick. Using a 3-inch cookie cutter, form 8 biscuits.
Top the chicken mixture with the biscuits and brush the dough with the remaining 2 tablespoons buttermilk. Bake until browned and cooked through, about 25 minutes.
