How can I split and trim a string into parts all on one line?

Try

List<string> parts = line.Split(';').Select(p => p.Trim()).ToList();

FYI, the Foreach method takes an Action (takes T and returns void) for parameter, and your lambda return a string as string.Trim return a string

Foreach extension method is meant to modify the state of objects within the collection. As string are immutable, this would have no effect

Hope it helps ;o)

Cédric