If you can't find gomashio in an Asian market (or the Asian aisle of your local grocery store),you can easily make your own by lightly toasting a tablespoon of sesame seeds with a pinch of sea salt in a skillet for about a minute, shaking the skillet frequently to avoid scorching the seeds.
Arrange a steamer basket in a large pot with about an inch of water. Cover, and bring water to a boil. Add broccoli to the steamer basket, cover and steam, tossing once or twice, until just tender, about 4 to 5 minutes. Transfer broccoli to a large bowl.
Mix together the gomashio (or 1 tablespoon toasted sesame seeds and a pinch of sea salt), lemon juice, and sesame oil. Drizzle over the broccoli and toss gently to cover broccoli evenly with the dressing.