To make the polenta: Bring the water/stock to a simmer in a pot and whisk in the polenta. Add the salt and then bring to a gentle simmer, continuously whisking. When the polenta starts bubbling, turn the heat down, cover and allow to cook for 10-15 minutes until the polenta is thick, creamy and soft (taste a small amount to make sure there is no hard, gritty pieces left). Stir in the butter then remove the pot from the heat and allow to sit, covered, for another 10 minutes.
For the shrimp/prawns: Combine the shrimp with the oil, paprika and salt and mix well. Heat a large skillet/pan then fry the prawns in batches (to avoid overcrowding the pan) until golden brown on both sides. Remove and set aside.
Melt the butter in the pan and add the garlic and jalapeño and allow to cook for 30 seconds. Add the lemon juice and the shrimp back into the pan and allow to cook for another minute or two. Scatter over the parsley and serve over the polenta.