Lumpia have the three qualities that's helped street food, food trucks in particular, carve out a thriving niche in the culinary world: portability, convenience and variety. Usually described as a Filipino version of spring rolls, lumpia are ground meat and veggies packed neatly inside a simple egg-and-cornstarch wrapper that's shallow-fried to golden-brown goodness. Lumpia's compact size and ingredients freeze well, and frozen lumpia take just a couple minutes longer to cook than their freshly made brethren. You have to get the interior steaming hot without scorching the outside, though, so making sure you have the oil at the ideal temperature range helps ensure they cook evenly all the way through.
Fill a straight-sided saute pan, commonly known as a sauteuse, with 1/2 inch of frying oil, such as peanut, sunflower or coconut oil, which is the all-purpose cooking fat in most Filipino kitchens.
Set the heat to medium-high and let the oil heat up for about 10 minutes. To check the temperature of the oil, drop a 1-inch cube of white bread in it and time how long it takes for it to brown. A 1-inch cube of white bread turns golden brown in 60 seconds in 350- to 375-degree-Fahrenheit oil, exactly where you want it when frying. If the bread browns in less than a minute, or takes longer than a minute, adjust the burner so it crisps up in 60 seconds exactly.
Remove the lumpia from the freezer and unwrap them. Only take enough lumpia from the freezer that you can fry in the pan at one time while giving them about 3/4 inch between each other.
Grasp the frozen lumpia one at a time with tongs and place them in the oil. Use the tongs to keep the lumpia away from each other in the oil during the first 30 seconds of frying to prevent them from sticking to each other.
Scoop a little oil in a 2-ounce ladle or large spoon and pour it over the lumpia while cooking. Spoon-basting speeds cooking up a bit and helps shallow-frying foods cook evenly.
Fry the lumpia until golden brown all over and heated through, about 7 minutes. Roll the lumpia as needed using the tongs during frying.
Remove the lumpia from the oil one at a time using tongs and place them on a plate lined with paper towels.
Insert a probe thermometer in the side of a lumpia lengthwise and check the temperature. You should heat frozen food to at least 165 F. If the they measure low, place them back in the oil and cook them until hot and steaming.
Heat the oven to 425 F and remove the lumpia from the freezer.
Arrange the lumpia on a cookie sheet or in a shallow baking dish, spaced about 1 inch apart. Place the lumpia in the oven on the middle rack.
Heat the lumpia until the wrapper turns golden brown and crisps and the internal temperature reaches 165 F, about 12 to 15 minutes. Insert a probe thermometer lengthwise in side of a lumpia to check the temperature.