Heat the oil in a large pan to high heat. Add the cumin seeds and cook for 30 seconds to darken them.
Add the onion and stir. Cook for 3-4 minutes to soften.
Stir in the garlic, ginger, and chili peppers. Cook for 30 seconds to let the flavors bloom.
Add the potatoes and stir. Cook, stirring occasionally, for 5 minutes to slightly soften the potatoes.
Add the tomatoes and stir. Cook for 2-3 minutes.
Add the cauliflower, turmeric, paprika, mango powder and salt to taste.
Stir, then reduce heat to medium-low and cook for 30 minutes, stirring occasionally. Add a bit of water if the pan becomes too dry.
Remove from heat and season with garam masala and lemon juice (if using in place of mango powder). Adjust with salt.
Garnish with cilantro and serve.