Preheat the oven to 350 degrees. Line the bottom of a 9-inch tart pan with parchment paper. Grease the sides with oil or butter.
In a small food processor, add 1 egg, almond flour and salt, pulsing until combined. Optional to add 2 tablespoons of melted coconut oil. Pulse a few more times until a dough forms. Warning: it will be very sticky.
Transfer the dough to the center of the tart pan. Using a sheet of plastic wrap or greased palms, press the dough out into an even crust, coming just ¼ to ½ an inch up the sides. Bake in the oven for 8 to 10 minutes, until firm and beginning to brown. Remove and let cool.
Meanwhile, make the curd: in a medium saucepan, whisk the remaining 3 eggs and honey until smooth. Set the pan over medium-low heat. Add ¼ cup of coconut oil. Cook, whisking occasionally, until the oil is melted, about 2 minutes. Add the lemon juice and zest and continue cooking, whisking gently, until the mixture begins to thicken, about 5 minutes. Remove from the heat immediately and continue whisking to avoid any clumps.
Transfer the curd to the cooked tart crust and smooth in an even layer with your spatula. Allow to cool so the filling sets and serve at room temperature.