In a small bowl, whisk together the matcha powder and hot water. Let sit until it reaches room temperature.
In a large bowl, using a hand mixer set to high speed, whip the heavy cream until stiff peaks form, about 5 minutes. Beat in the green tea mixture and the sweetened condensed milk until just combined.
Transfer the mixture to a metal loaf pan and cover with plastic wrap. Freeze for 6 hours or overnight.
Make the magic shell:
Place chocolate chips and coconut oil in a microwave-safe bowl, and microwave on 50 percent power in 15-second increments until melted and smooth, stirring occasionally. Cool to room temperature before serving over green tea ice cream. Magic shell will quickly harden over ice cream as it cools. Sprinkle with black sesame seeds to garnish.