In a saucepan, saute bell peppers in oil over medium-high until softened and browning in places, 4 to 5 minutes. Add curry paste; cook until fragrant, about 30 seconds. Add stock; bring to a simmer. Add chicken and bok choy. Cook until bok choy is just wilted and chicken is heated through, about 1 minute. Remove from heat. Stir in lime juice. Season with salt and pepper.