Working with as many green beans as you can at once, chop them into small pieces (1/4-in long or smaller).
Peel and dice the potatoes into ~3/4-in cubes (you can leave the skin on if you prefer).
Select the Saute button (normal) on the Instant Pot or heat a non-stick pan on medium heat.
Add and heat the cooking oil, then add the mustard seeds, asafoetida, and minced garlic (if using). Fry for a few seconds.
Add the chopped green beans, diced potatoes, ground turmeric, red chili powder (if using), and 1/4 teasp salt (add more later). Mix well.
For Instant Pot Method: Add all the water, mix well, and close the Instant Pot lid. Select the Pressure Cook button to cook on high pressure. Set the timer for 2 minutes. When the time is up, allow the pressure to release naturally for only 5 minutes, and then manually release the rest of the pressure. Open the lid and set to Saute mode again (normal).
For Stove-top Method: Add half the water, cover the pan with a lid, and cook on medium-low heat until the potatoes and green beans are cooked and tender (about 10-15 minutes, potatoes should remain intact). Stir occasionally. During this time, if the water dries out, be sure to add 1 tbsp at a time as needed to cook and keep the green beans and potatoes from sticking to the pan.
Once the green beans and potatoes are cooked and tender, add the ground cumin and ground coriander.
Mix well and cook uncovered on medium heat for an additional 2-3 minutes. Stir occasionally and burn off most of the excess liquid remaining.
Add salt to taste and a small amount of freshly squeezed lemon juice. Mix and garnish with finely chopped fresh cilantro.
Serve hot with rice, Naan, or roti.
Notes
Long Green Beans - For this Gujarati recipe, I specifically love using the yard long beans if I can make my way to my local Asian market. But you can easily sub for any other green bean variety.Spices - Asian stores sometimes have both ground cumin and ground coriander combined into one spice packet. If this is the case, add the sum of the combined amount. Asafoetida (hing)
Omit if you do not have this spice.
Although this powder is naturally gluten-free, it is almost always manufactured by diluting it significantly with wheat flour. There are some brands you can find that make it with rice flour. If you are uncertain and have a strict gluten-free diet, then omit this ingredient.
Kid-Friendly Version - Omit the cayenne or red chili powder if needed.