1/3cupfreshly squeezed lemon juicefrom about 2 medium lemons
Place a rack in the center of your oven and preheat the oven to 375 degrees F. Coat a 9x13-inch pan with nonstick spray.
Dissolve the gelatin in the boiling water. (I measured the water into a large measuring cup, then stirred the gelatin right in. You could also do this in a heatproof bowl.) Let cool to room temperature.
In a medium mixing bowl or the bowl of a stand mixer fitted with the paddle attachment, beat together the oil, applesauce, and eggs until combined. Beat in the cooled gelatin. Reduce the speed to low, then slowly add in the cake mix, stopping as soon as the dry ingredients disappear.
Pour the batter into the prepared pan. Bake for 25 to 30 minutes, until the top springs back lightly when touched and a toothpick inserted in the center comes out clean with just a few moist crumbs clinging to it.
While the cake bakes, in a medium bowl, whisk together the powdered sugar and lemon juice until smooth.
While the cake is still warm, use the tines of a fork to poke holes all over the top. Pour the glaze slowly and evenly over the top, allowing it to drip down into the holes. Let cool to room temperature. Enjoy warm or hot with plenty of fresh berries and whipped cream.