"Mandarin" in American Chinese restaurants refers to a general style of cooking, but it's not regional like Szechuan or Cantonese styles. It roughly can be translated to mean "Royal", which really doesn't do much to define it other than that it should be rich and satisfying.
So a Chinese American restaurant dish labeled "Mandarin" probably won't have oranges in it.
The dish you describe sounds to me like an combination of dishes - sort of like Sesame chicken made with breast instead of thigh meat, like General Tso chicken but not spicy, and like chinese chicken salad but with the meat cooked like a main dish but just layered onto some lettuce. Most likely the dish never occurs in China proper. It's more likely to be one of those "syncretic" dishes that evolved in America to satisfy local tastes and notions.
Personally I don't care for most breaded chicken in chinese dishes - often the breading gets to be overdone and too chewy. Instead I coat the bite size pieces of chicken in a mixture of water, salt, sherry, chopped garlic, minced hot pepper, and cornstarch. Then stir fry it quickly in a fair amount of hot good quality cooking oil (I like safflower) until just cooked on the outside (it should be all white). Set aside, drain off oil, return oil to wok. Then toss in any fresh vegetable you like, cut into bite size pieces. Cook until veggies are almost done. Return the chicken back into the wok for final cooking - won't take long, don't overcook it. Drain off excess oil again before serving or adding more gravy. At the last if you like a thicker gravy add some more of the above marinating mixture and some soy sauce to taste, stir till it thickens. Serve over rice or on a lettuce leaf if you like.
You could substitute any sort of breading mixture (egg, flour, salt) for the cornstarch marinade.
The key here is just to sear the outside of the chicken, set it aside, and then cook the veggies, which take longer. If you were to try to cook the veggies and the chicken together the chicken would get overdone and tough. The cornstarch marinade gives the chicken a very light outer coating that helps to seal in the juices.
I usually add some sesame seed oil at the last minute, to taste, as well. If you like ginger, you can also add some slices (to be removed when serving) at the start, or some finely grated ginger that will remain.
I've been told that in traditional chinese cuisine the main component is almost always a vegetable. The meat is usually a minor component, almost just for flavoring. This no doubt goes back to the frugal availability of meat in traditional Chinese culture. Here in America food is so much more plentiful, and Americans expect large amounts of meat to dominate any main course, so recipes have changed to accommodate that expectation.
The cool thing about wok cooking is that once you use basic principles - fast heating and cooking, basic seasonings, don't overcook the meat, etc... you can mix and match ingredients as they are available or you prefer. It's very flexible and there is no one right way to do it, IMHO. Don't overload the wok so that the oil no longer sears the ingredients - then you might as well just simmer everything in a saucepan instead. You can also start adding ingredients found at chinese groceries, like real chinese greens, chinese broccoli, long beans, etc. Bottled or canned oyster sauce is popular but I generally prefer the taste of fresher ingredients.
I've found the above basic technique works for just about any meat - chicken, fish, pork, beef, shrimp, etc, or vegetable. Most of the time spent in such cooking is in the prepartion - cutting the food into bite size pieces (easily handled by the diners with chopsticks), preparing the spices and marinades, etc. The actual cooking goes by quickly, usually in 10 minutes or less. Of course you want to have the rice or noodles ready in advance ;-).
Good luck!