Heating up cooked egg rolls without altering the texture and flavor can be difficult, since the outside can become too crisp while the inside remains cold. On the other hand, the wrapper can become soggy while the inside dries out. Heat your egg rolls based on the cooking utensils you have available to make them crisp outside and warm inside -- just like when they were freshly cooked.
Preheat the oven to 450 degrees Fahrenheit.
Line the bottom of a baking dish or baking tray with aluminum foil. Lightly brush the aluminum foil with vegetable oil or cover it with cooking spray to keep the egg roll from sticking.
Place the egg roll in the oven on the center rack. Allow it to heat for five minutes.
Flip the egg roll with a pair of long tongs. Heat the egg roll for an additional five minutes on the other side.
Remove the egg roll from the oven and allow it to rest for two to three minutes before serving.
Microwave and Stovetop Method
Place the egg roll in a microwave-safe container. Heat the egg roll on a high setting for 30 seconds.
Heat 1 tsp. vegetable oil in a nonstick skillet or cast iron skillet until very hot, but not smoking.
Place the egg roll in the hot oil and heat it for two minutes on each side.
Remove the egg roll from the hot oil and allow it to rest for two to three minutes before serving it.