1 tablespoon tamarind paste
2 pounds freshly ground chicken breast
1 tablespoon canola oil
4 garlic cloves, minced
1 large shallot, thinly sliced
1 teaspoon (or more) roasted Thai chile powder
1/2 cup palm sugar or brown sugar
1/3 cup fresh lime juice
1/4 cup fish sauce
2/3 cup thinly sliced red onion
3 scallions, thinly sliced on the bias
1/2 cup fresh mint leaves, divided
4 tablespoons roasted rice powder, divided (available in specialty shops or see instructions below)
1 large carrot, peeled, thinly sliced into rounds
4 ounces long beans, cut into 3-inch lengths (about 1 cup)
1/2 head cabbage, leaves separated
1/2 head romaine lettuce, leaves separated and cut crosswise in half
Stir the tamarind paste and 1/4 cup of warm water in a small bowl until the tamarind dissolves and forms a tamarind juice. Spoon the juice into a large bowl; and discard the tamarind seeds.
Mix the chicken into the tamarind juices. Let stand for 15 minutes. Heat a large wok over medium-high heat. Add the oil. When the first wisp of white smoke comes off of the wok, add the garlic and shallot and stir until fragrant, about 30 seconds.
Add the chicken and cook until the chicken is cooked through, about 4 minutes. Reduce the heat to low. Stir in 1 teaspoon of the roasted Thai chile powder, adding more if desired. Stir in the palm sugar, lime juice and fish sauce. Add the red onion, green onions, 1/3 cup of the mint leaves and 3 tablespoons of the roasted rice powder. Give the mixture a good toss and remove from the heat.
Transfer the larb to a platter. Sprinkle with the remaining 1 tablespoon of roasted rice powder and garnish with the remaining mint leaves. Arrange the carrot, long beans, cabbage, and lettuce on a large plate. Serve the larb and the vegetable plate. Eat the vegetables between bites of larb to cool the palate, or use the lettuce and cabbage leaves to form cups to fill with the larb, carrots and long beans.