1. Heat oven to 425 degrees F and coat a mini muffin tin with cooking spray. Using a 2-inch round cutter, cut puff pastry into 48 rounds. Press rounds into the pan and prick bottoms with a fork; transfer to freezer while preparing filling.
2. Heat 1 tbsp of oil in a skillet over medium-high heat; add lamb and cook until browned, breaking up large chunks, about 3 min. Stir in tarragon, chives, cumin and garlic powder; transfer to a bowl. Add remaining oil to the skillet and cook shallots and carrots over medium-high heat, 2 min. Add corn and cook 5 min. Return meat mixture to pan and stir together. Mix in peas and season with salt and pepper to taste.
3. Scoop a small amount of the filling into each puff pastry cup. Bake until pastry is golden brown, 18 to 20 min. Let cool slightly before removing pies from pans.
4. Transfer mashed potatoes to a piping bag filled with a star tip and pipe a dollop on each pie.