Soften the dates: Preheat the oven to 350°F (180°C) and lightly grease a 9-inch (23 cm) square or 8 × 11-inch (20 × 28 cm) rectangular baking dish.Put 1 cup Medjool dates (pitted) in a bowl, cover with 1 cup boiling water, and soak for 10 minutes. Mash with a fork into a soft paste, leaving some chunks. Keep the soaking water.
Mix the wet ingredients: In a large bowl, mash 1 ripe banana with a fork. Add 1 cup Greek yogurt, ½ cup milk, 1 large egg, 1 teaspoon vanilla extract, 1 teaspoon cinnamon, and the softened dates with their soaking water. Stir until combined.
Add the oats: Stir in 2 cups rolled oats, 1 teaspoon baking powder, ½ cup chopped pecans, and ¼ teaspoon salt until everything is well mixed.
Bake the oatmeal: Pour into the prepared baking dish and spread evenly. Bake at 350°F (180°C) for 30–35 minutes, until the edges are set, the top is lightly golden, and the center is soft but not wet.
Make the date caramel: While the oatmeal bakes, soak ¾ cup Medjool dates in ¾ cup hot milk for 10 minutes. Add ¾ teaspoon vanilla extract and 1 pinch salt, then blend until smooth and creamy. Add more milk, a little at a time, until the sauce is easy to spread.
Add the topping: Let the oatmeal cool for 10 minutes, then spread the date caramel evenly over the top. Slice into squares and serve warm.