Place the sliced onions in a large bowl.
Add salt, red chili powder, turmeric, green chilies, mint or coriander, and dried pomegranate seeds if using. Mix well and let the onions rest for 10 to 15 minutes, until they soften and release some moisture.
Add besan, rice flour, and cumin seeds if using. Mix well so the flour coats the onions evenly.
In a small bowl, dissolve baking soda in 2 to 3 tablespoons water.
Add this to the onion mixture little by little. Mix gently to make a thick batter that clings to the onions. Add only as much water as needed.
Heat oil in a kadai or deep pan over medium heat. Test with a small bit of batter; it should rise steadily without browning too quickly.
Drop small portions of the onion mixture into the hot oil using your fingers or 2 forks. Do not overcrowd the pan.
Fry in batches, turning as needed, until the pakoras are crisp and deep golden brown on all sides.
Remove with a slotted spoon and drain on paper towel or a wire rack.
Serve hot with chutney or sauce of your choice.