Bring 1 inch of salted water to a boil in a large pot with a tightly fitting lid.
Using a steamer basket if available, steam the lobster tails until just cooked through–the meat should be opaque white and the shell should be bright red, about 6 minutes. Set lobster tails aside.
Once cool enough to handle, remove the meat from the shell by pushing through from the flipper end to the larger end of the lobster tail. Discard the shell.
Chop the tail meat into 1” pieces and set aside.
Trim the ends of the cucumber and slice lengthwise in half.
Remove seeds and pulp with a spoon.
Place the side of a large knife on the cucumber, skin side up, and smash. Slice into bite-sized pieces.
Cook the mushrooms (optional). In a large skillet over medium high heat, heat 2 Tbsp oil. Add ½ cup mushrooms and let brown undisturbed, about 3 minutes. Stir and continue to saute until deep brown, about 5-6 minutes. Let the mushrooms cool before mixing.
Combine the smashed cucumber, chopped lobster tail, mushrooms, and the Omsom starter into the mixing bowl, and stir to mix evenly.
Season with salt.
Serve with white rice and garnish with cilantro. Enjoy!