Heat a pan over medium heat. Sauté the curry paste with half of the coconut milk until fragrant and the oil separates. Add the remaining coconut milk and chicken, and cook until the chicken is just done.

Add water. When it comes to a boil, add the potatoes and onions. Transfer to a pot and simmer over low heat until the potatoes are cooked and tender.

Season with coconut sugar and fish sauce. Taste and adjust as needed. Bring to a boil, then remove from heat.

Beat the egg. Dredge the marinated pork in flour, then dip in the beaten egg. Repeat the flour and egg coating once more. Finally, coat with panko breadcrumbs. Fry over medium heat until golden and crispy on both sides. Drain on paper towels. Let cool slightly, then slice into pieces.

To serve, place the fried pork on hot steamed rice. Spoon the curry over the rice. Pour the cucumber relish into a bowl with the prepared cucumber, chili, shallot, and cilantro. Serve with the curry rice and tonkatsu.