Start by preparing the carrot and radish. Add the julienned carrots and sliced radish to a large bowl and toss in the sugar, salt, and vinegar. Set aside for 1 hour, stirring occasionally.
Next, prepare the marinade for the chicken and shallots. In the bowl of a food processor, add 2 tablespoons of the oil, the fish sauce, oyster sauce, chilli flakes, sugar, garlic, lemongrass, and lime zest. Process until smooth. Add to a bowl, along with the chicken and echalion shallots, and toss to coat in the marinade. Cover, transfer to the fridge, and marinate for 1-4 hours.
Once marinated, heat the remaining 2 tablespoons of oil in a large frying or griddle pan over a medium-high heat. Sear the chicken and shallots for about 5 minutes on each side, or until cooked through, this may need to be done in batches. Remove to a chopping board and slice the chicken into strips.
Cut the baguettes to the lengths you want for each sandwich. Slice the baguette pieces lengthways.
Spread each sandwich with the sauces (pate, mayonnaise, soy sauce, and hot sauce) and then layer with the pickled vegetables, coriander, and cucumber. Top with the chicken and shallots and enjoy.