Spray a 12-count muffin pan with cooking spray. Mold biscuits to the shape of each muffin cup. Par-bake biscuits for 6 to 8 minutes until light golden. Remove from oven and set aside.
Heat the oil in a large skillet over medium heat. Add ground beef and brown. Stir in the onions, salt, pepper and garlic and allow to cook together for a couple of minutes.
Mix flour into the meat mixture and stir until a paste consistency is reached. Add beef stock to pan and stir in vegetables and herbs, the last few minutes, until combined.
Reheat mashed potatoes in a microwave for 5 to 6 minutes. Stir in granulated garlic and onion powder.
Spoon equal amounts (approximately 2 tablespoons) of warm potatoes on the bottoms of each par-baked biscuit. Then top with equal amounts of beef mixture (approximately 2 tablespoons). Finally top with equal amounts of Cheddar. Return to oven and bake for 12 to 15 minutes until cheese is melted and browned. Remove from oven and allow to cool slightly before popping individual pies out with a knife.