In a bowl, make the sauce: whisk together the garlic, ginger, soy sauce, mirin, fish sauce, lime juice and sesame oil. Set Aside.
Season the chicken cubes with ½ tsp salt. In a large pan, heat 1 tablespoon vegetable oil until shimmering, add the shallots and sauté for a few minutes until slightly golden.
Add the chicken breast and cook for 1 minute on each side, until golden. (it will not be fully cooked and that is fine)
Add the sauce mixture and simmer for 3-4 minutes until the chicken is coated and fully cooked through.
To serve, place chicken in lettuce leaves; top with water chestnuts, cucumber, red pepper, cilantro and cashews.
Finish these off with a squeeze of fresh lime juice.