Earlier this year when I ate there with my folks for dinner, my brother ordered the steak and shrimp scampi, which was delicious. The entree was less than $20 as well, and I don't even remember where the last time I saw a surf and turf type dish for less than 20 bucks.
Even heartier is their prime rib. Oddly enough this diner is my go-to spot for prime rib! Yep, not some fancy steakhouse! It's at least a 24 oz cut, a huge portion and I always end up having to take some home. For a diner the prime rib is prepared pretty well (it's rare that they don't cook it to the requested temp and overcook it, etc.) At about $17 it's also the most reasonably priced prime rib I've seen.
I also love their Greek salad starter, which comes with a stuffed grape leaf (love em!) and anchovies upon request.
There's plenty of dining options on Rt 22 in the Union area, but Union Plaza diner is always a solid choice.
Union Plaza Diner
2466 Rt 22
Union NJ 07083