Given the following XML:
abcText1cba
abcText2cba
Your current xpath should be correct. Here is an alternative but ugly one.
XmlNodeList nodes = doc.SelectNodes("//span/parent::li/span[contains(text(), 'Text1')]/parent::li");
We find all the span-tags. Then we find all the li-tags that has a span-tag as child and contains the 'Text1'.
OR simply:
//span[contains(text(), 'Text1')]/parent::li