Toast hazelnuts in a dry skillet over medium heat until fragrant, 3 to 4 minutes. Set aside.
Warm milk and water in a medium saucepan over medium heat. Stir in salt and cinnamon; bring to a gentle simmer.
Stir in oats. Cook, stirring often, until creamy and tender, 6 to 8 minutes.
Fold in cherries, vanilla, and orange zest. Simmer 1 to 2 minutes to plump the fruit.
Remove from heat; swirl in butter and maple syrup. Cover and rest 2 minutes to thicken.
Spoon into bowls. Top with toasted hazelnuts, reserved cherries, and a dollop of yogurt if you like.