In a saucepan, mix 1-1/2 cups sugar, cornstarch, flour, and salt. Gradually add hot water, stirring constantly.
Cook and stir over high heat until mixture comes to a boil. Reduce heat; cook and stir 8 minutes longer. Remove from heat.
Stir small amount of hot mixture into egg yolks, then return to hot mixture. Bring to boiling and cook 4 minutes longer stirring constantly. Add butter and lemon peel. Slowly add lemon juice, mixing well.
Pour into prepared coconut flour pie crust.
Top with meringue.
Preheat oven 350°
Place egg whites and cream of tartar in the bowl of a stand mixer fitted with the whisk attachment. Beat egg whites unit soft peaks form and then gradually add sugar and continue beating until stiff peaks form, approximately 1-2 minutes. Spread on top of the lemon filling making sure to spread the meringue to touch pie crust all around the edges, sealing in the filling.
Bake for 10 minutes or until meringue is golden brown.