The issue with filling in the NOTCH, not the hole in the door is that when the door latches shut, there'll be pressure pressing on it from the rubber weather seal, so generally, a plastic filler piece for the spotlight notch, like for filling the antenna holes in the roof/trunk, would be a poor solution, since it's likely to get pushed right back out.
A far better solution there is what I've always recommended for the roof and trunk holes, weld in new metal and do proper body work.
1988 Ford Escort Pony 4-spd Eeyore (died of old age)
1993 Ford CVLX Ol' Blue (technicly totalled, now parts car)
1981 Suzuki GS550LX Blue on Black (eBay Special, still cleaning it up)
2003 Ford CVPI Morgan (former Morgan Co, IN sheriff's cruiser)
"The reasonable man adapts himself to the world; the unreasonable one persists in trying to adapt the world to himself. Therefore all progress depends on the unreasonable man." -- George Bernard Shaw