For the marinade, place the soy, 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, then pour into a frying pan and bring to a simmer.
Add the lemon juice and zest, thyme and chiles and simmer until thickened and reduced slightly, another 5 minutes. Remove from heat and leave to cool. Once cooled, transfer to a measuring jug so it's easy to pour; remove and discard the chiles.
For the tuna and pork, place the tuna steaks and pork chops into separate resealable bags.
Pour half of the cooled marinade in with the tuna steaks and the other half in with the pork. Add the sage leaves to the bag with the pork chops. Make sure everything is well coated before sealing both bags and placing in the fridge to marinate.
When ready to cook, grill the pork chops until cooked, 3 to 4 minutes on each side. Drizzle the beer over the pork while cooking for an authentic SA braai flavor.
Grill the tuna steaks for a minute per side, or longer if you prefer it cooked through.