Heat 2 tablespoons oil in a 12" skillet over medium-high heat. Add the onions and cook, stirring until soft, about 6 minutes.
Transfer onions to a bowl and add the shrimp, both flours, parsley, baking powder, paprika, a dash of salt and 5 tablespoons water and stir to combine thoroughly. Set batter aside to rest for 10 minutes.
Using the same skillet, add the remaining oil and place over medium-high heat. Working in batches, use 2 tablespoons of the batter for each fritter and cook, flipping once until golden brown and crisp at the edges, about 3 minutes.
Using a spatula, transfer the fritters to paper towels to drain and immediately season with flaky salt like Maldon and freshly ground black pepper.
Serve with lemon wedges and remoulade sauce. Squirt the lemon on the fritters, dip in sauce and enjoy.