Vigorously whisk together 1 cup of the oat milk, the vinegar, and cornstarch in a small bowl until the cornstarch dissolves. Add the remaining 1 cup milk. Set aside and let the magic happen while you prep everything else.
In a large bowl, whisk the flour, matcha powder, sugar, baking powder, and salt. Give it a quick whisk so everything is evenly distributed and looking nice and green.
Make a well in the center of your dry ingredients. Pour in the oat milk mixture, the water, oil, and vanilla. Stir until just combined — lumps are fine, overmixing is not. Let the batter rest for a couple of minutes while your waffle iron heats up.
Grease your waffle iron with cooking spray, if needed, then scoop the batter in and cook according to your waffle maker's instructions. When they're golden, crisp, and smell like a dream, they're done.
Serve topped with coconut whip, berries, sprinkles of matcha, and maple syrup.