Optimization problems

So i am having this really bad optimization problem and i was thinking people on the forums could help.

Note: the inside the mesh its empty its just the out side. it would be nice to reduce the verts by like 5000. This is the script i use to generate a face for a chunk. public void DrawBrick(int x, int y, int z, byte block) {

         Vector3 start = new Vector3(x, y, z);
         Vector3 offset1, offset2;
         
         if (IsTransparent(x, y - 1, z))
         {
             offset1 = Vector3.left;
             offset2 = Vector3.back;
             DrawFace(start + Vector3.right, offset1, offset2, block);
         }
         
         if (IsTransparent(x, y + 1, z))
         {
             offset1 = Vector3.right;
             offset2 = Vector3.back;
             DrawFace(start + Vector3.up, offset1, offset2, block);
         }
         
         if (IsTransparent(x - 1, y, z))
         {
             offset1 = Vector3.back;
             offset2 = Vector3.down;
             DrawFace(start + Vector3.up, offset1, offset2, block);
         }
         
         if (IsTransparent(x + 1, y, z))
         {
             offset1 = Vector3.forward;
             offset2 = Vector3.down;
             DrawFace(start + Vector3.right + Vector3.up + Vector3.back, offset1, offset2, block);
         }
         
         
         if (IsTransparent(x, y, z - 1))
         {
             offset1 = Vector3.right;
             offset2 = Vector3.down;
             DrawFace(start + Vector3.back + Vector3.up, offset1, offset2, block);
         }
         
         
         if (IsTransparent(x, y, z + 1))
         {
             offset1 = Vector3.left;
             offset2 = Vector3.down;
             DrawFace(start + Vector3.up + Vector3.right, offset1, offset2, block);
         }
         
         
     }
     
     
     public void DrawFace(Vector3 start, Vector3 offset1, Vector3 offset2, byte block)
     {
         int index = verts.Count;
         
         verts.Add (start);
         verts.Add (start + offset1);
         verts.Add (start + offset2);
         verts.Add (start + offset1 + offset2);
         
         BlockType blockType = Terrain.blocks.GetBlock(block);
         float zoom = 0.125F;
         
         Vector2 uvBase = blockType.uv;
         
         if(blockType.sideTexture == true)
         {
             if ((offset2 == Vector3.down))
             {
                 uvBase = blockType.side;
             }
         }
         if(blockType.bottomTexture == true)
         {
             if (!(offset2 == Vector3.down) && !(offset1 == Vector3.right))
             {
                 uvBase = blockType.bottom;
             }
         }
         
         uv.Add(uvBase);
         uv.Add(uvBase + new Vector2(-zoom , 0F));
         uv.Add(uvBase + new Vector2(0F , zoom));
         uv.Add(uvBase + new Vector2(-zoom , zoom));
         
         tris.Add (index + 0);
         tris.Add (index + 1);
         tris.Add (index + 2);
         tris.Add (index + 3);
         tris.Add (index + 2);
         tris.Add (index + 1);
     }

Thank you.