For the biscuit dough: Using a pastry blender or two table knives, cut the shortening into the flour in a medium bowl until it resembles coarse meal. Use a fork to stir in the buttermilk to make a soft dough, or until the dough comes together and leaves the sides of the bowl. Continue stirring with the fork until all the flour is worked into the dough, and then turn the dough onto a lightly floured board and knead three or four times until smooth and manageable.
For the meatloaf: Preheat the oven to 450 degrees F. Grease a baking sheet with cooking spray.
Combine the beef, onion, salt and pepper in a large skillet and cook over a medium heat until the meat is browned, 12 to 15 minutes. Remove from the heat and stir in the flour and 1/3 cup of the reserved tomato liquid. Remove 1 cup of this meat mixture and set aside. Add the tomatoes and the peas to the remaining mixture in the skillet. Set aside.
On a well-floured surface, roll the biscuit dough into a large rectangle about 1/2 inch thick. Spread the reserved cup of meat mixture thinly over the dough, and then roll the dough like a jelly roll, beginning from one long edge. Place the roll on the prepared baking sheet. Using kitchen shears or a very sharp knife, cut 1-inch slices almost through to the bottom of the roll. To expose some of the filling, pull alternate slices to the left and right. Bake until browned, about 15 minutes
Reheat the beef and vegetable mixture. Slice the baked loaf and spoon some of the hot vegetable and meat mixture over each slice.
Adapted from Georgia Cooking in an Oklahoma Kitchen by Trisha Yearwood (c) Clarkson Potter 2008