Rinse the spinach or kale thoroughly and set aside.
In a medium saucepan, bring the water or milk to a simmer over medium heat.
Add the rolled oats and a pinch of salt to the saucepan, stirring to combine.
Cook the oats for about 5 minutes, stirring occasionally until soft.
While the oats are cooking, blend the spinach or kale with the banana and chia seeds.
Once the oats are cooked, remove them from heat and stir in the green mixture until fully combined.
Taste the oatmeal and adjust sweetness, if desired, by adding honey or maple syrup.
Serve warm, garnished with additional toppings like nuts, seeds, or fresh fruit as desired.