Preheat oven to 350 degrees F.  Oil an 8 or 9 inch square pan.

In a large bowl, whisk together oil, eggs, and mashed bananas.  Whisk in vanilla, flour, baking powder, cinnamon, ginger, and cardamom until just combined.  Pour into the prepared pan.

Slice each of the remaining bananas in half horizontally.  Then slice each half in half again, but this time lengthwise, following the natural curve of the banana.  Press the banana pieces decoratively into the batter, cut side up.  Generously brush the bananas with the lemon juice.

Bake the cake about 40 minutes until golden brown and a toothpick inserted in the center comes out clean or with a few moist crumbs.  Serve warm or cool completely in the pan.  Cake may be stored in an airtight container at room temperature for up to 5 days or frozen, wrapped in parchment and foil and placed in a zipper bag for up to 3 months.  Thaw at room temperature about an hour or in the microwave about 1 minute.