Preheat the oven to 350 degrees F (175 degrees C).
Heat oil in a pot over medium-low heat. Season chicken with salt and pepper and add to hot oil. Stir in onion, 2 tablespoons curry paste, garlic, harissa, onion salt, and garlic powder; cook until onion is soft and chicken is browned, about 5 minutes. Stir in enough cornstarch to thicken. Pour in 1 can of coconut milk. Add remaining curry paste and pumpkin. Reduce heat to low, cover, and cook for 10 minutes.
Uncover and add peas, beans, and chile pepper. Stir in brown sugar, lime juice, fish sauce, and sea salt. Pour in remaining can of coconut milk.
Transfer the mixture into a 2-quart baking dish or oven-safe bowl. Arrange biscuits on top of the filling. Brush tops with beaten egg.
Bake in the preheated oven until biscuits are golden brown, about 20 minutes.