Batch Zooming Images with GIMP

Save below code to file "~/.gimp-2.8/scripts/images-scale-and-fit-canvas-to-layers.scm" and restart GIMP to use:

(define (images-scale-and-fit-canvas-to-layers in-width in-height)
  (map (lambda (image)
         (gimp-image-scale image in-width in-height))
       (vector->list
        (car
         (cdr
          (gimp-image-list))))))

(script-fu-register
 "images-scale-and-fit-canvas-to-layers"
 "Images Scale and Fit Canvas to Layers"
 "
 1. Open images
 2. Filters=>SunDawning=>Images Scale and Fit Canvas to Layers
 3. Click to make Images Scale and Fit Canvas to Layers
 
 Equivalent to:
 
 1. Open image
 2. Scale
 3. Right Click
 4. Image=>Fit Canvas to Layers
 5. Repeat the above process to scale all images
 "
 "SunDawning"
 "Copyright (c) 2018 https://steemit.com/@SunDawning"
 ""
 ""
 SF-ADJUSTMENT "Width" '(1366 1 100000 1 10 0 1)
 SF-ADJUSTMENT "Height" '(768 1 100000 1 10 0 1) )

(script-fu-menu-register "images-scale-and-fit-canvas-to-layers" "/Filters/SunDawning")