Heat sesame oil over medium heat in a large saucepan. Saute onion and garlic in the hot oil until garlic begins to brown, 3 to 4 minutes. Add potatoes, carrots, curry paste, ginger, fish sauce, chile paste, and coriander; stir until evenly coated and well mixed.

Stir coconut milk and 1/2 cup water into the saucepan. Season with salt and pepper. Cover, reduce heat to low, and simmer for 10 minutes. Stir in chicken, zucchini, and bell pepper. Continue to simmer, covered, until chicken is no longer pink in the center, about 5 minutes more.

Dissolve cornstarch in remaining 1/2 cup water in a small bowl; stir into the simmering mixture. Uncover, raise heat to high, and bring to a boil. Continue to boil for 3 to 4 minutes. Remove from heat. Stir in cilantro and lime juice just prior to serving.