Mix the tahini with 1 tbsp milk and 1 tbsp water. Put the oats, 1 sliced banana, cardamom, 100ml milk and 300ml water in a pan with a pinch of salt. Cook over a medium heat for 5 mins, stirring, until creamy and hot.
Divide between two bowls. Pour over the remaining milk, then top with the remaining sliced banana. Drizzle over the tahini mixture and sprinkle over the toasted sesame seeds.