Heat 2 to 3 inches of oil in a wok, kadhai/karahi, or dutch oven over medium heat to 350°F (180°C).
To a medium bowl add the chickpea flour, salt, baking soda, garam masala, cumin seeds, turmeric, and chili powder. Mix and then add 1/4 cup water. Adding 1 tablespoon of the water at a time just until you have a batter the consistency of heavy cream and it coats a spoon.
While the batter is resting, thinly slice the onion, grate the potato, and mix together in a large bowl with fresh cilantro, lemon juice, green chili, and ginger (if using).
Add the flour batter into the vegetables and mix well. Don’t let this mixture sit too long, or the liquid from the onions and potatoes will seep out, and your batter will become watery.
Line a baking tray with paper towels.
Heat your oil over medium-high heat in a wok or pan with high sides and pour the oil until it is two to three inches deep. If you aren't used to deep frying, please be careful. Test that your oil has come to 350°F (180°C) with a thermometer, or until a bit of the batter pops up to the surface immediately and is frying nicely.
Turn the heat to medium and very carefully drop spoonfuls of the mixture into the oil. Do not crowd them and turn them several times until they are golden brown and crispy. This will take about 5 to 10 minutes. Turn the heat up a bit if the oil isn't bubbling gently.
Using a slotted spoon, remove the pakoras and drain on the paper towels. As you fry the pakoras in several batches, you may need to increase, or lower the heat as needed to keep the oil at approximately 350°F (180°C).
These potato pakoras freeze beautifully and if you want to work ahead for a party, make a batch or two, and freeze in a zip lock bag. To heat up again, place in a 350° oven for 5 to 10 minutes, and heat until warmed through and crispy.
Make sure your onion slices are not longer than 2 inches.
Other vegetables ideas are zucchini, eggplant, cauliflower, paneer, tomatoes, cabbage, corn, red bell pepper (capsicum), or spinach.
Seafood, chicken, or even tofu pakoras are also tasty.
If you do not have chickpea flour (besan), substitute a 50/50 mix of all-purpose flour and cornstarch makes a good substitution, though I do encourage you to find besan if you can.
Pakoras are best eaten hot out of the oil, as they lose their crispness.
A candy or deep-frying thermometer comes in handy here but is not absolutely necessary.
Additional flavorings to play around with:
Curry leaves instead of cilantro
A pinch of asafoetida (hing)
A 1/2 teaspoon of carom seeds (ajwain)
1 to 2 teaspoons of dried fenugreek leaves (kasoori methi) crushed
Chaat masala to dust the fritters after coming out of the oil