Combine the onion, green chili peppers, cilantro, and mint in the bowl of a food processor. Use the pulse setting to finely chop (but not blend) this mixture. Transfer to a large bowl.
Add the cooled beef and lentil mixture from the Instant Pot to the food processor. In batches, process this mixture until smooth. Then add to the large bowl with the chopped onion mixture. Mix well, then taste and add salt, if desired. Add the whisked egg and mix to combine.
Using your hands, shape ¼ cup heaped of the mixture into a flat, round patty about 2 3/4 inches in diameter. Continue with the rest of the mixture. You will have around 20-22 patties. If you wish to freeze them, do so at this point.*
Place the egg in a shallow bowl so that you can dip the kababs as you cook. Heat a large skillet, frying pan, or cast iron pan over medium-high heat. Add enough oil to coat the bottom of the pan.
Dip both sides of each patty into the egg wash. Place 3-5 patties in the pan and allow them to cook for 3-4 minutes on each side, using a spatula to turn them over. Be careful not to crowd them too much or it will be harder to turn them. Reduce heat as necessary.
Remove from the pan, and place on a plate lined with a paper towel to absorb any extra oil. Repeat until you have finished pan-frying all the patties. Cook any leftover egg in the remaining oil and serve with the patties.