In a bowl, soak rice in water for 20 minutes. Drain.
In a 3-quart heavy saucepan, bring coconut milk, milk, sugar and rice to a gentle boil. Reduce heat and simmer, uncovered for 25 minutes, stirring occasionally.
Remove from heat and add lime zest. Serve at room temperature or chilled. Sprinkle with toasted coconut, if desired.