Prep the Cabbage: Remove any tough outer leaves, quarter the cabbage, and slice out the hard core. Finely shred the leaves into ⅛-inch / 3mm slivers.
In a large bowl, toss the shredded cabbage with the finely chopped green chilies.
Bloom the Spices: Heat the oil in a wok or large skillet over medium-high heat.
When the oil is hot and shimmering, add the mustard seeds.
Once they start to pop (this happens quickly!) , carefully add the crushed curry leaves—be ready for them to splutter.
Cook the Cabbage: Immediately add the cabbage and chili mixture to the pan.
Stir-fry continuously for 2-3 minutes, just until the cabbage has wilted slightly but is still crunchy and bright green.
Finish and Serve: Lower the heat, stir in the salt and lemon juice, and mix well.
Taste and adjust seasoning as desired, then turn off the heat and serve.