For the blueprint marinade: Place the kecap manis, brown sugar, olive oil, ginger, garlic and tomato paste into a food processor, and blitz to a paste. Add the water and blitz again until well combined.
Pour the marinade into a frying pan, sprinkle with salt and pepper, and bring to a simmer. Add the lemon juice, lemon zest, thyme and chiles. Simmer until thickened and reduced slightly, 5 minutes. Remove from the heat and leave to cool.
Once cooled, transfer to a measuring jug, so it's easy to pour, then remove and discard the chiles.
For the surf and turf: Place the tuna steaks and the pork chops in separate resealable plastic bags. Divide the cooled marinade between the bags. Add the sage to the bag with the pork chops. Make sure everything is well coated before sealing both bags and placing in the fridge. Marinate for at least 1 hour.
When ready to cook, grill the pork chops for 3 to 4 minutes on each side, until cooked through. For an authentic South African braai flavor, drizzle the beer over the pork while cooking.
Grill the tuna steaks for 1 minute per side, or longer if you prefer them cooked through.