Remove beef from refrigerator 1 hour before cooking to reach room temperature.
Make your marinade. Put lemongrass, garlic, ginger, brown sugar, soy sauce, Knorr seasoning, calamansi juice, oil, water, and black pepper in a blender. Blend everything until smooth. Taste and add salt if needed.
Place your beef in a ziplock bag. Pour all the marinade over the beef, making sure the meat is fully covered. Seal the bag and refrigerate overnight.
Make your dipping sauce by mixing cane vinegar and sweet chili sauce in a bowl. Set aside.
Take your marinated beef and let excess marinade drip off on a wire rack. Pat the meat dry with paper towels. Keep the marinade - you'll need it later.
Get your charcoal grill ready. You want it at 190°C (375°F). Keep the hot coals on one side of the grill.
Heat up a heavy pan until very hot. Sear your beef for 3-4 minutes on each side until it's nicely browned.
Move the beef to the cool side of your grill (away from the coals). Close the lid and cook for 45-50 minutes. Every 15 minutes, brush some of the saved marinade on the meat.
Once done, let the meat rest for 15 minutes. Then slice it thinly against the grain.
No hooded grill? No problem. Cook the beef in your oven at 190°C for the same time. After it's cooked, place some wood chips or charcoal in a fireproof container and light them. Put your beef in a larger covered container with the smoking chips for 15 minutes to get that smoky flavor.
Serve your sliced beef with the dipping sauce and enjoy!