To prepare the dough:

In a small bowl, dissolve the yeast in the lukewarm water.  Let it stand for about 10 minutes untill it is thickened and bubbly.

Meanwhile, sift the flour into a large bowl and make a well.  Once the yeast is proofed, pour it into the well.  Add sugar, salt, eggs, lemon or orange zest, and vegan butter.

Knead all the ingredients together until a soft dough forms that no longer clings to the sides of the bowl.

Shape the dough into a ball and cover it with a dish towel. Let it rise for an hour and a half.

For Filing and Baking: 

Preheat oven to 350℉.  Line a few baking trays with parchment paper. 

Flour a clean work surface.  Roll the dough to about ¼-inch thick. Cut rounds of dough with the edge of a drinking glass or circle cookie cutter, dipped in flour.

Place a dollop of jam on each round.  Pick up the sides and pinch them together to form a triangle, allowing for the jelly centers to remain exposed. 

Place the hamantaschen about 1-inch apart on the trays and brush the tops with a beaten egg.  Set aside to rise for 30 minutes.

Bake for about 20 minutes until gently browned. Serve with sprinkled powdered sugar.

Notes:

This dough can be made by hand or using a stand-mixer with a dough hook.