Rinse cucumbers and strawberries well with cold water. Trim ends then cut cucumbers into 1/4-inch thick slices. Hull strawberries then halved lengthwise. Place cucumbers, strawberries and onion in large glass bowl. Set aside.
Mix remaining ingredients in medium saucepan. Bring to boil on medium-high heat, stirring to dissolve sugar and salt. Reduce heat to low; simmer 5 minutes. Let stand 5 minutes to cool slightly. Pour over cucumber mixture.
Refrigerate at least 2 hours or until ready to serve.