Preheat the oven to 400°F (200°C).

Heat oil in a wok over medium-high heat.

Brown the lamb in the wok.

Place the lamb on an oiled wire rack in a roasting pan.

Combine kecap manis, sesame seeds, and half of the crushed garlic.

Brush the mixture over the lamb.

Roast for approximately 25 minutes, or until the lamb reaches the desired doneness.

Let the lamb rest, loosely covered with foil, for 5 minutes.

Slice the lamb thickly.

While the lamb is roasting, heat oil in the same wok over high heat.

Stir-fry the grated ginger and remaining crushed garlic until fragrant.

Add the sliced red pepper and chopped gai lan to the wok.

Combine oyster sauce, lime juice, and 2 tablespoons of water.

Pour the sauce mixture over the vegetables.

Stir-fry until the gai lan is just wilted.

Serve the sliced lamb on top of the gai lan mixture.