Make a stir-fry with your favorite veggies, a stir-fry sauce, and the steak thinly sliced. Like mudbug said add the steak towards the end of stir-frying because of it alread being cooked.
or
Saute some sliced bellpepper and onions, then add the steak long enough to get it warm and serve it all on French rolls. You could also make French Dip sandwiches.
or
Make fajitas with sauted onions and bellpepper with your favorite fajita seasoning.
or
This recipe is great for leftover steak. Again you will have to adjust the cooking times due to your steak already being cooked.
Chinese Pepper Steak
1 lb. round steak
1 medium onion, sliced
1 bell pepper, cut in strips
2 tablespoons oil
2 envelopes Au Jus gravy mix
4 teaspoons soy sauce
½ teaspoon ginger
½ cup water
3 cups cooked hot rice
Cut meat in half lengthwise with sharp knife and then crosswise into thin slices. Cook steak, onion, and bell pepper in hot oil until meat is browned. Drain and place back in skillet. Stir in other ingredients except rice. Add more water, if needed. Cook 5 minutes, stirring occasionally. Serve over hot rice.