Probably there are many ways to do this. The first thing I’m thinking of:
To create a yellow oval with a greyed out background, you can duplicate the track. The upper track gets reduces opacity (e.g. levels of 50%) and a secondory color corrextor with the saturation set to nearly zero.
The lower track gets he cookie cutter fx with the choice for e.g. OVAL and CUT AWAY ALL BUT SELECTION and a feather as you like. The lower track also gets a secondary color corrector which you use to make the beam yellow.
You can keyframe the position the beam wherever you like in the small white square in the FX popup window.
Theo