Bring a large pot of water to a boil.

In a medium bowl, whisk together green tea, soy sauce, rice vinegar, sugar, dark sesame oil, ginger, and red pepper flakes to make the dressing.

Set the dressing aside.

Drop soba noodles into the boiling water and stir to prevent sticking.

Cook noodles until just tender, about 3-4 minutes.

Drain the noodles and rinse with cold water.

Drain the noodles again, shaking the colander to remove excess water.

Transfer the noodles to a large bowl.

Drizzle the noodles with 2 teaspoons of dark sesame oil and toss to coat.

Add half of the dressing to the noodles and toss to coat.

In a large shallow serving bowl, combine watercress, jicama, cucumbers, and scallions.

Add the remaining dressing to the watercress mixture and toss to coat.

Push the watercress salad to the perimeter of the bowl.

Mound the noodles in the center of the bowl.

Sprinkle with sesame seeds and serve at room temperature.