Preheat oven to 375°F. Fit crust into a 9-inch pie dish, crimp edges, and prick the bottom with a fork. Line with parchment, fill with pie weights, and bake for 15 minutes. Remove weights and bake 8-10 minutes more until golden. Cool completely.
In a medium saucepan, whisk together water, sugar, cornstarch, and salt until smooth. Cook over medium heat, whisking constantly, until the mixture comes to a gentle boil and thickens, about 5-7 minutes. Remove from heat.
Whisk in lemon juice, zest, and turmeric (if using). Add vegan butter and stir until melted and smooth. Strain the filling directly into the cooled crust to remove any lumps.
Press plastic wrap directly onto the surface of the warm filling to prevent a skin from forming. Refrigerate for at least 3 hours, until fully set.
In a clean, dry mixer bowl, beat aquafaba on medium speed until foamy, about 1 minute. Add cream of tartar and salt, then increase to high. Beat 4-5 minutes until soft peaks form.
Slowly stream in powdered sugar with the mixer running. Add vanilla and continue beating 2-3 minutes until glossy and stiff peaks form.
Spoon meringue over the chilled filling, spreading to the edges of the crust to seal. Create peaks and swirls with the back of a spoon. Brown with a kitchen torch or under the broiler for 1-2 minutes.
Let the pie rest for 10 minutes before slicing. Dip a sharp knife in hot water and wipe dry between cuts for clean slices. Serve chilled or at cool room temperature.