To make the filling, heat 2 Tbsp of the oil in a medium saucepan. Add the sausage and onion and cook, stirring often, until the onion is translucent, about 5 minutes. Add the garlic, squash, cassava, chili, and curry powder and cook, stirring often, until the garlic is golden, about 3 minutes. Add the coconut milk, chicken stock, and tarragon and bring to a simmer, then reduce the heat and simmer gently for 35 minutes
Drain the vegetables and reserve the liquid. Transfer the vegetable mixture to a bowl and mash with a fork, adding half of the reserved cooking liquid, or as needed, to make a smooth puree. Season with salt, then set aside to cool
Lay a butterflied shrimp out on a sheet of plastic wrap, cover with another sheet, and gently pound with a meat mallet to as thin as possible, about 1/8 inch or less. Remove the top piece of plastic wrap and place 1 1/2 tsp of the filing in the center of the shrimp. Bring the 4 edges of the plastic wrap together up over the shrimp,so the shrimp wraps around the stuffing, and then, holding the edges of the plastic wrap, squeeze the wrap around the shrimp to form it into a ball, then rotate the shrimp ball to tighten it. Repeat with the remaining shrimp
Heat the remaining 2 Tbsp oil in large saute pan, preferably nonstick, over medium-high heat. Carefully remove the plastic from the shrimp balls. Add them to the oil (seams side down), in batches if necessary, and cook for 3 minutes. Turn and cook for additional 4 minutes, or until the shrimp is opaque throughout