Soak split moong in water for at least 6 hours or overnight.
Wash the moong and discard most of the skin. If moong is well soaked, the skin will peel off from split moong when rubbed between fingers. I discarded ⅔ – ¾ of the skin.
Transfer moong to a colander or a strainer and let the water drain.
Meantime, grind together chilies, ginger, salt and cumin seeds. Onions can also be ground but I forgot and used chopped onion instead. This step is optional. These can be ground with moong dal as well but to get a fine paste, I usually tend to grind these separately in a mini grinder.
Transfer ground paste to a food processor or a blender. I would recommend a food processor for garelu or vada as it would not require too much water when grinding. Then add washed and drained moong dal, keeping aside ¼ – ⅓ cup of dal.
Grind everything to a paste. It need not be a smooth paste. If necessary, add about 1 – 2 tablespoon water and no more than that. I used 1 tbsp. water. Also, if onion is ground, water is not required and moisture from ground onion is sufficient to grind the dal.
Transfer ground dal to a bowl, add chopped onion (if not used in previous step), scallion, cilantro, methi leaves, spinach if using, and chili powder. Add the moong dal that was kept aside and mix well.
Taste the dal mixture and adjust chili powder and salt to taste.
Heat oil in a pan for deep frying.
Take a Ziploc bag and place small lime sized dal mixture on it. Press it into a disc using fingers and make a hole in the middle using the index finger.
When oil is hot, gradually drop the garele in oil. 4 – 5 garelu can be deep fried at a time, depending on the size of the pan.
Deep fry on medium to medium high heat until garelu are light brown and cooked inside.
Remove from oil and drain on paper towels.
Repeat the process with rest of the dal mixture.
Serve garelu with butter.