Add the oil to your pan turn the heat up to medium heat.
As the oil is heating, add the cumin, mustard seed, and curry leaves and let them cook for a minute or two, taking care not to burn the spices.
Next, add the turmeric and allow it to cook for another minute or so, continuing to stir. (Cooking the turmeric is an important step because raw turmeric is rather bitter, and cooking it helps to cut the bitterness almost completely.)
Add the ginger, garlic, and onions. Sauté until the onions start to get soft.
Add the zucchini and any other vegetables you may like and add salt to taste.
Stir fry until the zucchini just starts to soften. Remove from the heat and serve immediately.