Remove the outer papery skin around the tomatillos and rinse them thoroughly. They tend to be sticky, so make sure to thoroughly clean them. Dry them completely, before finely dicing them.

In a clean, dry dish, add chili powder, mustard powder (grind mustard seeds in the spice grinder or blender) and salt. Mix well.

Add vinegar, tomato pieces and oil (you can use any oil sesame seed oil, vegetable, canola etc.). Mix well with a clean, dry spoon.