For the pound cake, heat the oven to 350ºF. Coat a 9- by 5-inch loaf pan with cooking spray and then dust the pan with flour to coat, tapping out the excess.
In a medium bowl, whisk together the flour, ground ginger, baking powder, baking soda, and salt.
Using an electric mixer on medium speed, beat the butter with the brown sugar until soft and fluffy, 4 to 5 minutes. Beat in the fresh ginger, then the eggs, one at a time. Change to low speed and beat in half of the flour mixture. Beat in the sour cream, then the remaining flour mixture.
Scrape the batter into the prepared pan and smooth the top. Bake until a toothpick inserted in the center comes out clean, 50 to 60 minutes. Cool the cake in the pan on a rack for 10 minutes. Unmold the cake and place it directly on the rack to cool completely.
For the compote, bring the water and sugar to a boil in a large saucepan over medium heat. Meanwhile, use a vegetable peeler to remove the zest from the lemon in one continuous strip (or smaller strips if the zest breaks as you work). Add the lemon zest and rhubarb to the sugar syrup and cook for 1 minute. Remove the pan from the heat and stir in the strawberries, vanilla extract, and cinnamon. Cover and let stand until the rhubarb is soft but still holds its shape, about 1 hour. Remove the lemon zest and use the compote immediately or refrigerate it for up to 4 days.
To serve, cut the pound cake into roughly ½-inch-thick slices, toast the slices, and serve them with the compote.
Tip: If you don’t have rhubarb, replace it with 2 pounds (about 3 pints) of raspberries and/or blueberries.