Whisk together the lime juice, lemon juice, soy sauce and maple syrup in a small bowl. Set aside.
Heat the oil in a large skillet over medium heat. Add the scallions, shallots, lemongrass and chili. Cook until vegetables just soften, about 5 minutes.
Add the ground seitan and cook an additional 2-3 minutes until warmed through. Add the dressing to the pan and cook until the liquid has been absorbed and the mixture is crispy and tender.
Stir in the mint and season to taste with salt/pepper and crushed red pepper, if desired.
Separate the lettuce leaves and spoon the larb mixture on top. Serve as is or as a side to rice.