Heat the oil in a deep pan or karahi (wok) and add the cumin seeds and onions. 
Fry the onions until they start to caramelize and turn brown.
Add the ginger, garlic and tomatoes. Cook until the tomatoes break down and soften. You can add a splash of water if the masala is too dry.

📝Notes:

➡️1. Don't add too much water in vegetables. Veg will turn mushy.
➡️2. Chop or dice the vegetables into small even sized pieces to allow for uniform cooking. 
➡️3. You can substitute with other vegetables like bell peppers, baby corn, mushrooms or cabbage.

➡️4. You can use frozen vegetables too in this recipe, but remember not to add any water in this case. 
➡️5. For a spicy curry, add a couple of slit green chillies and a pinch of garam masala.