In saute pan over medium-high heat, heat oil. Add cumin seeds and saute until seeds begin to pop, 20 to 30 seconds.
Add gingerroot and garlic. Saute until aromatic, 20 to 30 seconds.
Add onion. Saute until translucent, 3 to 5 minutes.
Add curry paste and tomatoes. Sauté 2 minutes.
Add cauliflower, water and salt. Bring to a boil. Reduce heat. Simmer until cauliflower is tender-crisp, 4 to 5 minutes.
Add steamed potatoes. Return to a simmer and cook until heated through, 4 to 5 minutes. Stir in cilantro.
Serve with cooked rice, if desired.
Notes
For steamed potatoes: Peel and dice potatoes, place in steamer basket over boiling water. Steam until potatoes are fork-tender, about 4 to 6 minutes. Drain.