Combine lemongrass, shallot, soy sauce, sugar in a bowl. Marinate beef for 30 minutes. Drain beef from marinade.
Place shallots on paper towel lines sheet pan for 30 minutes.
Heat a pot with the oil to 275°F. Fry shallots in batches until golden brown, drain, and reserve. Cool the oil.
Mash the garlic and chilies in a mortar and pestle with the sugar until smooth. Transfer to a bowl and add fish sauce, lime juice and water. Drizzle in the shallot oil until incorporated.
Heat a grill or griddle on high and grill or griddle the beef until just done. Slice thinly.
Toss mango, green beans, bell peppers, cilantro, and Thai basil with chili lime vinaigrette.
Place lettuce in bowls and top with the salad and beef. Garnish with fried shallots and peanuts.
*Recommended mango ripeness stage 2 to 2.5
Created by The Culinary Institute of America as an industry service to the National Mango Board.