If you've made it all the way through the TTR Legends Cup, a good place to go for this achievement is the final combat race on Back to the 80s. There are 7 laps and 7 other drivers in this race, giving you plenty of time to set yourself up.
What you want to do is find and pick up the EMP power-up (I went with level 2 to be safe). Once you have it, park yourself just past the finish line and hold
to look behind you. This is a long, wide-open stretch that will give one of the other drivers plenty of room to get a shot off and the chance for you to see it coming. Once here, just wait for the other drivers to race around and one of them is bound to pick up a homing missile that they will use on you. When a driver fires and you see it get close, hit
to deploy the EMP. Do your best to time it before it hits you, but I was still able to get the trophy even though I was late on my timing.
I was lucky and got an EMP as my first power-up before the end of the first lap. After parking past the finish line, both the driver in first and in second had homing missiles the next time they passed me (the first driver didn't use it). The earlier you get the EMP and get to this spot, the more chances you give another driver to pick up a homing missile.
Hopefully this solution helps! If it's not straightforward enough, let me know and I can amend my solution to better help.