Preheat oven to 340°F (170°C) and adjust oven rack to middle position. Generously grease and flour a 9-inch springform bundt pan
Mix wet ingredients: In a large bowl, whisk the eggs and sugar with a hand mixer until pale and fluffy, about 2 minutes. While whisking, slowly pour in the olive oil, followed by the orange juice, Grand Marnier liqueur (if using), and vanilla extract.
In a separate bowl, whisk together the flour and baking powder.
Gradually add the dry ingredients to the wet ingredients, whisking gently until just combined. Be careful not to overmix.
Bake: Pour the batter into the prepared bundt pan. Bake for about 40-45 minutes, or until a toothpick inserted into the centre comes clean.
Let the cake cool in the pan for 10 minutes before inverting it onto a wire rack to cool completely.
Make the glaze: In a small bowl, whisk together the powdered sugar, Amaretto liqueur, and orange juice until smooth. Add more orange juice 1 teaspoon at a time to thin as desired.
Once the cake is completely cool, drizzle the glaze over the top or dust with powdered sugar.