Roast the potatoes. Pierce 3 medium sweet potatoes and roast at 400 degrees F for 40 to 45 minutes until soft throughout.
Stir the sauce. Combine the peanut butter, lime, soy sauce, half the chili, coconut milk, sugar, coriander, half the green onions, and lemongrass paste.
Cool, halve, and scoop. Rest the potatoes 10 minutes, halve them lengthwise, and scoop out the flesh, leaving the shells intact.
Crisp the shells. Bake the empty skins on a tray for 5 minutes until dry and firm.
Mash and fill. Mash the flesh with the sauce, fill the shells, and bake 10 minutes until hot.
Garnish. Top with the reserved chili, green onions, and chopped peanuts and serve warm.