Prepare the shrimp by peeling, deveining, and rinsing them. Pat dry.

Mince the onion finely.

Cook the somen noodles according to package instructions, rinse under cold water, and drain.

Heat sesame oil in a pan, add garlic and sauté until fragrant. Add minced onion and cook until softened.

Add butter and shrimp to the pan, stirring until the shrimp are coated and cooked through.

Add the cooked somen noodles to the pan and stir-fry. Season with fish sauce, salt, and pepper, mixing well.