Bring all ingredients to room temperature 30 minutes before cooking. This ensures even cooking of the meat.
Roughly chop your beef into small pieces - aim for about ¼ inch size but don't worry about making them perfect. The different sizes add nice texture to the dish. Pat the meat dry with paper towels to help it brown better.
Get your wok or deep pan really hot - heat your coconut oil until you see the first wisps of smoke. Add the beef in a single layer and let it brown for 3-4 minutes on each side at high heat (200°C/400°F). Don't stir it around - letting it sit creates a nice crust.
Turn the heat down to medium-high. Toss in your onions, garlic, ginger, and chilies. Cook these for about 2-3 minutes until you can really smell the aromatics and the onions turn clear. As you stir, break up any larger pieces of meat.
Lower the heat to medium and pour in your coconut milk. Add most of your cherry tomatoes (save some pretty ones for garnish). Let this come to a gentle bubble, then turn down the heat and let it simmer for 5 minutes. You'll see the sauce start to thicken.
Add your green beans and let everything cook for another 3-4 minutes. You want the beans to stay crisp but turn bright green. Season with fish sauce, black pepper, and a good squeeze of lemon juice.
Turn off the heat and let everything rest for 5 minutes - this lets all the flavors come together nicely. Taste and add more fish sauce or lemon juice if needed.
Serve in bowls over hot rice, topped with your saved tomatoes and fresh cilantro. The sauce should be creamy but still loose enough to soak into your rice.
Remember: if your sauce gets too thick, add a splash of warm water. If it's too thin, let it simmer a bit longer. The perfect Tinaktak sauce should coat the back of your spoon but still flow easily.