Heat the ghee or oil in a large saucepan over medium heat. Add the onion and cook until softened, about 5 minutes. Add the garlic and ginger paste and cook for another minute.
Add the garam masala, cumin, coriander, turmeric and chili powder (if using). Stir to combine.
Add the carrots, potatoes and peas. Stir to combine.
Add the tomatoes and 1/2 cup of water. Bring to a boil, then reduce heat to low and simmer for 15 minutes or until vegetables are tender.