North Dallas, my recommendations:
Mediterranean (Middle Eastern as you call it, specifically Lebanese):
1) Fadi's. The only drawback IMO is the cafeteria style serving of the salads and veg, but many of the meats, especially the kebabs, are cooked to order.
http://www.fadiscuisine.com/index.htm
2) Ali Baba. Technically this is Richardson but it's along the North Central Expressway Corridor. They have a lunch buffet but other times everything is cooked to order. IMO, not as good as Fadi's but decent enough.
http://alibabamedgrill.com
There are other places, mostly in Richardson, off of 75, that are better. My favorite is Afrah. The food and atmosphere are great, you can get a hookah (pipe, not something else) and sit on the patio. The owner is often there and is a nice guy.
Thai
1) Royal Thai. Native Thai people will tell you this place isn't authentic because they tend to tone down the flavors for the American palate. Still good, atmosphere is great. This place gets very busy at lunch and dinner.
http://royalthaitexas.com/
2) I was going to list Toy's on Lemmon here but I just read that they had closed. Unfortunate.
Korean food
If you have a car, take the 35 exit to Royal Lane and go east or west, and you will find a ton of Korean restaurants.
1) Koryo Kalbi (formerly Chosun). Authentic Korean BBQ, this is arguably the best Korean BBQ in Dallas.
http://www.koryobbq.com/
2) Korea House. I have not had the Korean BBQ, but the bibimbap is good.
http://www.koreahousedallas.com/
Sushi
I love sushi but not my strong point in terms of knowing the best places. One of my favorites is:
Tokyo One - served buffet style but you won't find a better price for the variety of sushi and sashimi you get, and it's fresh, with the sushi chefs working behind the counters constantly.
http://tokyo-one.com/
Of course if you're from NC, and you're coming to Dallas, and you want ethnic, trying Tex Mex is a must. I won't even begin to form a list because an entire thread could be started and argued over where the best Tex Mex is in Dallas.
I'll be generic and say if it's your first time trying it, go to El Fenix. Established in Dallas in 1918, still a very consistent experience for a first timer.
http://www.elfenix.com/