To prepare the coconut curry sauce, drizzle vegetable oil in a medium saucepan over medium-low heat. Add the onion and cook, stirring occasionally, until beginning to soften, 10-15 minutes. Stir in the sugar and cook until caramelized, about 10 minutes. Add the garlic and cook just until fragrant, about 1 minute. Remove from heat. Place onion and garlic in a small bowl and set aside.
Wipe the saucepan and place over medium heat. Add the butter. Once melted, whisk in flour until golden, about 2 minutes. Stir in the curry powder, turmeric, paprika, chili powder, and tomato paste. Cook for another 2 minutes, then stir in coconut milk, chicken stock, garlic, and onions. Season with salt and pepper. Reduce heat to medium low and simmer for 10-15 minutes. At the end of simmering, add garam masala.
Cut each chicken breast in half to make 2 thin pieces. Flatten each piece with a meat tenderizer until they are about 1/2 inch thick.
In a small bowl, mix together the spice rub ingredients- Chinese five spice, salt, pepper, and curry powder. Set aside half the mixture and rub the flattened chicken pieces with the other half.
In a shallow bowl, combine the corn flour, flour, baking powder, and remaining spice rub. In another shallow bowl, beat together the egg. In a third bowl, add the panko breadcrumbs.
In a large wok or deep frying pan, pour in oil until it is 2 inches deep over medium heat. As the oil is heating, coat a piece of chicken in the flour, shaking off the excess. Coat in the beaten eggs, then the panko breading. Repeat with remaining chicken breasts.
Place breaded chicken in the thoroughly heated oil, a few at a time to not overcrowd, and fry until golden on each side. Adjust temperature as needed. Once occked through the middle and golden, remove to a towel limed plate. Repeat with remaining chicken.
Serve immediately over rice and top with coconut curry sauce.