Heat the olive oil in a 4-quart saucepan over medium heat until shimmering. Add the onions along with the salt and cook until they begin to turn golden, approximately 4 minutes. Add the garlic and cook for 1 minute longer. Add the tomatoes and bring the mixture to a boil. Decrease the heat to low and add the ginger, pepper, cardamom, and okra. Stir to combine. Cook, uncovered, for 20 minutes. Remove from the heat, taste, and adjust the seasoning as desired. Serve immediately.