In a small bowl, dissolve the yeast and 1 teaspoon of the sugar in the warm water. Let sit for 5-10 minutes until foamy.

In a large mixing bowl, combine the flour, remaining sugar, eggs, 2 tablespoons oil, lemon zest, vanilla, salt, and the yeast mixture.

Knead the dough by hand or with a mixer for about 5-7 minutes until smooth and elastic. If too sticky, add a sprinkle of flour.

Place the dough in a greased bowl, cover with a towel, and let it rise in a warm place for about 1.5 hours, or until doubled in size.

On a lightly floured surface, roll the dough out to 1/2-inch thickness. Use a round cutter or glass to cut out circles.

Place the dough circles on a lined baking sheet, cover loosely, and let rise again for 30 minutes until puffy.

Heat the frying oil in a deep pot to 350°F (175°C). carefully drop 3-4 doughnuts in at a time.

Fry for about 1-2 minutes per side until deep golden brown. Remove with a slotted spoon and drain on paper towels.

Once cool enough to handle, use a squeeze bottle or piping bag with a round tip to inject strawberry jam into the side or top of each doughnut.

Generously dust the filled doughnuts with powdered sugar before serving warm.