Divide up the broccoli florets and wash. In a bowl, toss them with the olive oil, sea salt, and freshly cracked black pepper.
In an oven heated to approx. 400 degrees F, bake the broccoli on a baking sheet. Check after 10 minutes and turn over if browning. Take out after 5 more minutes, or when tender.
For the dressing, put the tahini in a bowl. Juice half a lemon, being careful to exclude any seeds, and add to the bowl with the water. Whisk until it reaches a pourable dressing consistency, adding more water if necessary. Add salt and pepper to taste.
To serve, plate the broccoli and drizzle with the tahini dressing. Top with black or white sesame seeds if desired.