Dash in movement direction, not in forward direction

Hey guys, I implemented a jump-dash feature, but when I go backwards and dash, the player dashes forwards, instead I want him to dash backwards.

Here's the dash script:

isGrounded = Physics.CheckSphere(groundCheck.position, groundDistance, groundMask);

     if (Input.GetKeyDown(KeyCode.LeftShift) && !isGrounded)
     {
         if(canDash == false)
         {
         currentDashTime = 0;
         canDash = true;
         }
     }
     if(currentDashTime < maxDashTime)
     {
         moveDirection = transform.forward * dashDistance;
         currentDashTime += dashStoppingSpeed;
     }
     else
     {
         moveDirection = Vector3.zero;
     }
     controller.Move(moveDirection * Time.deltaTime * dashSpeed);

     if(isGrounded)
     {
       canDash = false;
     }

Thank you!