Preheat oven to 400°F.
Heat oil in a 10-inch cast iron skillet over medium until shimmering.
Add onion, carrots, and potatoes; cook, stirring frequently, over medium until carrots and potatoes are just starting to soften, 4 to 5 minutes.
Stir in garlic and ginger; cook stirring constantly until fragrant, about 1 minute.
Add stock and bring to a boil over medium-high, stirring occasionally; reduce heat to medium-low and simmer, stirring occasionally and adjusting heat as needed, until vegetables are fork tender, 8 to 10 minutes.
Stir in curry mix, ketchup, and salt until dissolved and mixture is thickened, about 2 minutes.
Stir in chicken until evenly distributed. Remove from heat and keep warm.
Roll pastry on a lightly floured surface into a 13-inch square.
Lay pastry over skillet; trim leaving a ¾- to 1-inch overhang.
Fold pastry under itself so rolled edge is flush with top edge of skillet; use the tines of a fork to crimp edge into side of skillet.
Brush top of pastry with beaten egg.
Cut 8 (1 ½- to 2-inch) slits in top of pastry to vent.
Bake until pastry is golden brown and filling is bubbly, about 30 minutes.
Let stand 15 minutes before serving.
