Wash the carrots and cut into slices. They will steam with no extra liquid so they need to be thin enough.
Measure and set out the peas.
Make the ginger-garlic paste.
Chop finely the onions.
Measure the ground spices together, except garam masala.
Set a pot on high heat. Once hot, add in 2 tbs of oil or ghee and the cumin and mustard seeds. Let them sizzle and pop a little, then add the curry leaves and chopped onions. Reduce the heat to medium and fry for 2-3 mins. Then add the ginger-garlic paste and fry until the raw smell goes away. If using tomatoes, add them in now and fry them a little, too. Then add the ground spices and mix well.
Reduce the heat to low, add in the carrots, mix them with the masala, then cover the pot and let them steam without adding any extra liquid. Once the carrots are half-done, add in the peas and cover the pot again. Cook until done (al-dente carrots, cooked peas).
If no amchur was used, add in lemon juice (from about half a lemon), add a sprinkling of garam masala, chopped cilantro and adjust for salt.
Serve with dal and rice, roti or paratha.