Bring 1 cup water to a boil in a small saucepan and then pour in the couscous in one steady stream. Stir to prevent lumps. Turn off the heat, cover, and set aside for 15 minutes. Once liquid is absorbed, fluff with a fork.
In a heavy-bottomed pot, heat oil over medium heat. Add onion and cook until soft. Add garlic and cook for 1 minute. Add bell peppers and chili powder and cook for another minute. Stir in tomatoes and black beans and their liquid; bring all to a simmer and simmer for 5 minutes or until thickened. Add chicken and heat through. Stir in lime juice and cilantro and remove from heat. Serve over fluffed couscous.