Heat the olive oil in a skillet over medium heat, saute the onion until tender and starting to brown, stirring occasionally. Remove from pan heat and allow onion to cool slightly, but remain in the skillet.
While the onion cooks, stir the cardamom and ginger into the yogurt until well blended.
Pour the spiced yogurt into the skillet and stir in to the warm onion. Do not put over heat as it will cause the yogurt to separate. The warmth that remains in the skillet and the onions will warm the sauce sufficiently.