Separate the leaves from thick stems where necessary.
Leafy greens can contain considerable soil, so rinse them several times until the water is clean.
Roughly chop the mustard greens and spinach.
Add green chili, ginger, garlic, water, and salt.
Cover and cook over medium-low heat for approximately 20–25 minutes, stirring occasionally.
Use an immersion blender to blend them into a thick, rustic puree.
Avoid making the puree completely watery. Saag should have a thick, spoonable consistency.
Stir the mixture into the blended greens.
Allow the mustard oil to heat properly, then reduce the heat slightly.
Add cumin seeds and let them sizzle.
Cook for 1–2 minutes until fragrant.
Add chopped tomatoes.
Add turmeric, coriander powder, cumin powder, Kashmiri chili powder, garam masala, and salt.
Stir occasionally to prevent the saag from sticking to the bottom.
Stir gently and simmer for another 2 minutes.
Transfer the saag to a serving bowl.
Serve hot with makki di roti, roti, naan, paratha, or basmati rice.