Prepare the Cauliflower: Wash and dry the cauliflower thoroughly. Spread it out on a clean towel and let it air-dry for 1–2 hours so there is no moisture left.
Toast the Fenugreek: In a dry pan, toast the fenugreek seeds over low heat for 1–2 minutes until fragrant. Let cool, then grind to a coarse powder.
Make the Spice Mix: In a small bowl, combine the ground fenugreek, red chili powder, turmeric and salt.
Warm the Oil: Pour the sesame oil into a small pan. Add the sliced garlic (and mustard seeds, if using). Heat gently over low heat until the garlic just turns golden and the mustard seeds begin to pop. Remove from heat and let it cool to warm (not hot).
Mix the Cauliflower: In a large bowl, add the cauliflower and pour over the lemon juice. Stir to coat well.
Combine with Spices: Sprinkle the spice mixture over the cauliflower and mix thoroughly so every piece is coated.
Add the Oil: Pour the warm sesame oil over the cauliflower and stir gently to combine.
Store: Transfer to a clean, dry glass jar. Press down to remove any air pockets and seal with a lid.
Mature the Pickle: Leave the jar at room temperature for 24 hours so the flavors meld. Then refrigerate. It keeps for 3–4 weeks when stored cold.