Heat a small skillet over medium-high heat. Add the sesame seeds and toast for 1–2 minutes, stirring frequently, just until fragrant and lightly golden. Remove from heat and set aside.

In a small bowl, whisk together the water, soy sauce, sugar, and toasted sesame seeds. Set aside.

Bring a medium pot of salted water to a boil. Add the spinach and cook for about 1 minute, just until wilted. Drain into a colander and rinse with cold water to stop the cooking process.

Once the spinach is cool enough to handle, squeeze firmly to remove excess moisture. Transfer to a cutting board and roughly chop.

Add the spinach to a bowl, pour over the sesame dressing, and toss to coat. Adjust seasoning to taste. Serve immediately or chill until ready to eat.