GetProcessNameByExpression.cs

private static Func<Process, string> GetProcessNameAccessor()
{
    var param = Expression.Parameter(typeof(Process), "arg");
    var processInfoMember = Expression.Field(param, "processInfo");
    var processNameMember = Expression.Field(processInfoMember, "processName");

    var lambda = Expression.Lambda(typeof(Func<Process, string>), processNameMember, param);

    return (Func<Process, string>)lambda.Compile();
}

private static readonly Func<Process, string> _getProcessNameFunc = GetProcessNameAccessor ();
public string GetProcessNameByExpression()
{
    return _getProcessNameFunc(_process);
}