In a large pot or Dutch oven, heat the oil over medium heat. Add the chopped onion and sauté for about 3-4 minutes until translucent.
Add the bite-sized chicken pieces to the pot. Cook until the chicken is no longer pink, about 5-7 minutes.
Stir in the cubed potatoes and sliced carrots. Cook for another 3-4 minutes.
Add the yellow curry paste, grated ginger, and minced garlic to the pot. Stir well to coat the chicken and vegetables with the spices.
Pour in the coconut milk, stirring to combine. Bring the mixture to a gentle simmer.
In a small bowl, mix the cornstarch with a few tablespoons of water to create a slurry. Stir in the cornstarch mixture.
Add the fish sauce (if using), lime juice, and brown sugar. Stir well and let the curry simmer for an additional 10-15 minutes, or until the potatoes are tender.
Serve hot over cooked rice, garnished with fresh cilantro and sriracha.