Below is an example of 1) a background, 2) main image, 3) magnifying glass PNG and I would like to place his hot dog inside the magnifying glass, leaving just the background (and the glass with the hod dog of course).
In the past I would basically give the magnifying glass a background to mask the rest of the picture and knock out the red using chroma key but it's a bit limiting as you can't control (for example zoom in) the two layers independently.

With normal masking which I only tried the masked shape is enlarging together with the masked image, if you wanted something moving, zooming in inside the glass.

What kind of does the trick for me is then applying vignette with spotlight effect centering on the glass and removing the black around using another chroma key (so chroma key for red, vignette effect on the fat guy with cutting out the black with another chroma key).

I wonder if there is an easier or better way?