Add the remaining 1 tbsp oil and the onion and stir, scraping the bottom and sides of the wok to pull up any sticky bits from cooking the chicken. Add the shrimp paste and the remaining 3 tbsp kecap manis. Stir well and add the rice, tossing to break up any lumps. Stir-fry until the rice is warmed through, about 2 to 3 minutes. Taste the rice and season with salt and MSG, then return the chicken to the wok and cook for 1 minute more, or until the chicken is fully cooked through. Place the fried rice on a serving platter, garnish with the optional toppings of your choice, and serve.