Add the cauliflower, onion, and cucumber to the pot and allow to soak overnight.
Bring the mixture to a boil over medium-high heat; simmer until the vegetables are tender; drain.
Add the vinegar, flour, sugar, mustard powder, curry powder, and turmeric to the vegetables and bring to a boil; reduce heat to medium-low and simmer until the mixture thickens, stirring occasionally.
Ladle into sterilized jars; seal. Process in a boiling-water canner for 5 minutes.