DECLARE
order_number VARCHAR2(20);
order_row VARCHAR2(20);
part_number VARCHAR2(20);
BEGIN
order_number := &order_number
order_row :=&order_row
part_number :=&part_number

str :='order_number'||order_number||'order_row'||order_row||'part_number'||part_number;

TEST_PACKAGE_PROCESS_ORDER.START_PROCESS(str);

1. delimited string of value sets
2. refcursor
3. PL/SQL associative array
4. nested table type (collections)
5. xml data

"1,1,ABQ24X:1,2,PTZ91Y:1,3,PTZ92Y:2,1,AB24X"

"order_number,order_row,part_number:1,1,ABQ24X:1,2,PTZ91Y:1,3,PTZ92Y:2,1,ABQ24X"

1. string variables have limits in size (4000 bytes) (bigger on 12c as I recall but still an upper bound), and CLOBS are wieldy and hard to use if you use them to get around the size limit issue.
2. string manipulations are requires to parse the incoming data and get the pieces out and this is expensive compared to other methods.

declare
   sql_v varchar2(32000) := 'select order_number,order_row,part_number from yourtable where some_where_clause';
   c1 sys_refcursor;
   results_v ???
begin
   open c1 for sql_v;
   results_v := call_your_function (c1_p in sys_refcursor);
end;
/

declare
   type r1 is record (order_number integer,order_row integer,part_number varchar2(10));
   type t1 is table of r1 index by binary_integer;
   a1 t1;
   i binary_integer;
   results_v ???;
begin
   1 := 1;
   a1(i).order_number = 1;
   a1(i).row_number = 1;
   a1(i).part_number := 'ABQ24X';
   1 := 2;
   a1(i).order_number = 1;
   a1(i).row_number = 2;
   a1(i).part_number := 'PTZ91Y';
   1 := 3;
   a1(i).order_number = 1;
   a1(i).row_number = 3;
   a1(i).part_number := 'PTZ92Y';
   1 := 4;
   a1(i).order_number = 2;
   a1(i).row_number = 1;
   a1(i).part_number := 'ABQ24X';
   result_v := call_your_function (a1);
end;
/

create or replace type o1 is object (order_number integer,order_row integer,part_number varchar2(10))
/
create or replace type c1 is table of o1
/

declare
   c1_v c1 := c1();
   results_v ???;
begin
   select cast(multiset(select * from (
                                        select 1,1,'ABQ24X' from dual union all
                                        select 1,2,'PTZ91Y' from dual union all
                                        select 1,3,'PTZ92Y' from dual union all
                                        select 2,1,'ABQ24X' from dual
                                      )
                       ) as c1
              )
   into c1_v
   from dual;
   results_v := call_your_function (c1_v);
end;
/

Note I have used WHOLE OBJECT ASSIGNMENT in order to fill the nested table C1_V.

Declare
   type r1 is record (order_number integer,order_row integer,part_number varchar2(10));
   type t1 is table of r1 index by binary_integer;
   a1   t1;   
   --
  xmlvar  XmlType := XmlType('<?xml version="1.0" encoding="ISO-8859-1"?>
<Orders>
  <Order>    
    <OrdNum>1</OrdNum>
    <OrdLine>
      <OrdRow>1</OrdRow>
      <PartNum>ABQ24X</PartNum>
    </OrdLine>
    <OrdLine>
      <OrdRow>2</OrdRow>
      <PartNum>PTZ91Y</PartNum>
    </OrdLine>
    <OrdLine>
      <OrdRow>3</OrdRow>
      <PartNum>PTZ92Y</PartNum>
    </OrdLine>    
  </Order>
  <Order>    
    <OrdNum>2</OrdNum>
    <OrdLine>
      <OrdRow>1</OrdRow>
      <PartNum>ABQ24X</PartNum>
    </OrdLine>
  </Order>  
</Orders>  
'
);  
--  results_v ???; 
  Procedure ExtractXml(
    xmlp      In  XmlType,
    t_nt      Out t1    
  ) Is
  Begin
    Select t.OrdNum,
           u.OrdRow,
           u.PartNum
      Bulk Collect Into t_nt
      From XmlTable('/Orders/Order'
                    passing xmlp
                    Columns OrdNum  Number(2) Path 'OrdNum',
                            xLig    XmlType   Path 'OrdLine'
                   ) t,
           XmlTable('OrdLine'
                    passing t.xLig
                    Columns OrdRow  Number(2)    Path 'OrdRow',
                            PartNum Varchar2(10) Path 'PartNum'   
                   ) u;                           
/*
    For i In 1..t_nt.Count() Loop
      Dbms_output.put_line(t_nt(i).order_number||' '||t_nt(i).order_row||' '||t_nt(i).part_number);
    End Loop;                   
*/    
  End;
Begin  
  ExtractXml(xmlvar, a1);
-- result_v := call_your_function (a1);  
End;