Peel the hard outer layers of the lemongrass stalk until you reach the pale yellow inner layers. Cut off the bottom 2 inches of the stalk, which is the bulb. Finely slice 2/3 up the stalk. Save the top 1/3 of the stalk for future soups or broth.
Place sliced lemongrass and chunk of ginger in food processor. Pulse for 1 minute until finely chopped and almost pasty. Add in olive oil, hoisin, Sriracha, salt, and white pepper. Pulse a few more times until well mixed.
Place the sauce in a glass container and refrigerate until ready to use.
Bánh Mì
Slice the eggplant at a steep angle into 1/4 inch slices. Place the slices in a large bowl. Add cornstarch and salt to the bowl and toss eggplant until it is evenly coated.
Heat vegetable oil in a skillet until hot. It should be hot enough so that once the eggplant hits the oil it should instantly start to sizzle. Add in a few slices of eggplant to the pan. Do not overcrowd the pan, you want one single layer. Fry for 3 minutes on each side until crispy. Remove eggplant from the oil and allow to drain on a paper towel. Repeat until all the eggplant has been fried.
Toast the soft french rolls in the oven for about 4-5 minutes. Smear a little bit of the lemongrass sauce on the roll. Layer on a few slices of fried eggplant, add a little more sauce, then the pickled daikon and carrots, a few slices of jalapeño, and then a few bits of cilantro. Add more Sriracha or hoisin based on taste and enjoy!