4 -- chicken breasts, skinless and boneless (about 1 1/2 pounds), cut into 1-inch chunks
1-1/2 cup chicken broth
3 stalks lemongrass, chopped into 2-inch pieces
1 piece ginger, about 2 inches, coarsely chopped
1 teaspoon lime zest
2 tablespoons Thai fish sauce (optional)
1 tablespoon vegetable oil
2-1/2 tablespoon cornstarch
4 cups fresh pineapple chunks, about 1 inch each
1 teaspoon salt
2 tablespoons cilantro, chopped
2 tablespoons mint, chopped
Place chicken broth in small saucepan. Add lemongrass, ginger and lime zest. Bring to a simmer; cover and cook for 10 minutes. Stir in fish sauce (if using); set aside.
While the chicken broth mixture is simmering, warm vegetable oil over high heat in a large, non-stick skillet or wok. Toss chicken chunks in cornstarch. Add chicken to heated oil in two batches; sauté until golden brown, about 5 minutes. Remove chicken, place on plate and set aside. Add pineapple chunks to pan and sauté quickly, about 2 minutes.
Return chicken to skillet or wok. Pour chicken broth into pan through strainer, separating out lemongrass, ginger and lime zest pieces. Discard these pieces. Stir over high heat until sauce reaches simmer, about 1 minute. Reduce heat to low and simmer for 4 minutes, until sauce has thickened lightly. Add salt. Sprinkle with cilantro and mint. Serve immediately over rice or noodles.