Ginger Chicken with Watercress

Ingredients

• 1 bunch scallions, chopped
• 1 3 -inch piece ginger, peeled and roughly chopped
• 1/2 jalapeno pepper (remove seeds for less heat)
• 2 tablespoons packed light or dark brown sugar
• 1 tablespoon fish sauce
• 1 tablespoon soy sauce
• 1 tablespoon rice vinegar (not seasoned)
• 1 plum tomato, halved
• Kosher salt
• 6 skinless, boneless chicken thighs (about 21/4 pounds), quartered
• 4 ounces shiitake mushrooms, stemmed and quartered
• 2 bunches watercress, tough stems removed
• White rice, for serving