Combine lemongrass, palm sugar, shallots, garlic, soy sauce, fish sauce, sesame and vegetable oil and pepper in a large zip-top bag. Add lamb and marinate at least 2 hours, or overnight.
Bring rice wine vinegar and honey to a simmer in a small saucepan. Stir until combined and dissolved. Combine carrot and radish in a bowl and pour hot mixture over. Cool completely and chill until ready to serve.
Preheat oven to 350°F. Place lamb on a rack in a roasting pan and brush with some of the marinade. Fill pan with an inch of hot water, then loosely cover the lamb with foil. Roast for 1 hour, then remove foil and roast for another 45 minutes for pink or until cooked to your liking. Rest, loosely covered with foil, for 15 minutes. Slice lamb and set aside while assembling sandwiches, or cool the roast completely, unsliced, and chill until ready to serve.
Combine mayonnaise and chile sauce in a small bowl. Smear baguettes with mayonnaise mixture. Top with thinly sliced roast lamb, and drizzle with some of the mint sauce. Heat a thin layer of olive oil in a small skillet, fry some eggs, and drape them over the lamb. Top with pickled vegetables and finish with a drizzle of the mint sauce.