Preheat oven to 425 degrees Fahrenheit.

Pulse flour, powdered sugar, poppy seeds, and salt in a food processor until combined. Add Smart Balance and pulse until crumbly.

Add egg yolk and pulse until just combined.

Push dough into the pan and up the sides. Bake for 10 minutes. Clean the food processor.

Meanwhile, combine lemon zest with sugar in a small bowl until lumpy and fragrant.

Transfer to the food processor along with eggs, egg yolk, Smart Balance, vanilla, lemon juice, salt, and flour. Pulse to combine.

Slide out the rack with the tart crust and pour the filling directly into the crust. (This will save you from having to transfer a very full crust into the oven.)

Bake for 40 to 45 minutes until filling is set and the crust is golden.

Refrigerate until serving and dust top.