Combine water and rice in a small saucepan over medium-high. Bring to a boil, and reduce heat to low. Cover and simmer 20 minutes (do not uncover while cooking). Remove from heat, and let stand 8 minutes. Fluff with a fork, and transfer rice to a medium bowl.

Combine sugar and vinegar in a microwavable bowl, and microwave 35 seconds; whisk until sugar dissolves. Whisk softened cream cheese into vinegar mixture until combined. Fold cream cheese mixture into rice.

Line 12 muffin cups with 5-inch parchment paper squares coated with cooking spray. Using moistened hands, press 2 1/2 tablespoons of rice into each lined muffin cup, and shape up along sides. Chill 30 minutes. 

Beat heavy cream in a bowl with an electric mixer for 2 minutes. Add 1 cup of the Nutella, and continue to beat until soft peaks form. Fill each chilled rice cup with Nutella mixture, and chill 2 hours.

Top Nutella cups evenly with diced strawberries. Place remaining 1/4 cup Nutella in a ziplock plastic bag, and snip off a small piece of the bottom corner of bag. Drizzle Nutella over strawberries, and sprinkle with hazelnuts and flaky salt.