These are Matoa fruit (biological name Pometia pinnata), but the fruits are also known as tava, island lychee, Pacific lychee, Fijian longan, kasai, and buaha in different countries / regions.
Pometia pinnata is a tropical hardwood species that originated in Sri Lanka and the Andaman islands but is now found across southeast Asia including New Guinea and the Pacific islands.
Individual matoa fruits are a similar size to lychees but their skin is a thicker and hard shell that I needed to apply pressure to in order to crack open, and it broke into pieces that I pulled away from the fruit.
The peeled fruit looks like longan with similar translucent flesh but rather than spherical it's more of an oval lychee shape. You can see the reddish brown seed through the flesh, it looks almost pink.