Cut pineapple in half lengthwise, cutting from the root through the leaves.
Hollow out the pineapple by slicing around the perimeter, leaving a ½ inch (1 ¼ cm) border.
Slice the pineapple inside the cut border, and scoop out with a spoon. Repeat with the other half and set aside, as this will be the serving bowl for the salmon.
Add pineapple and water to a blender and blend until smooth.
Pour the pineapple purée into a saucepan over medium heat.
Add the sugar, rice wine vinegar, chili flakes, salt, and garlic to the pan and bring to a simmer. Stir frequently until sauce becomes lighter in color and slightly thickens.
In a small bowl, combine the arrowroot with the water to make a slurry. Add the slurry to the sauce and until the sauce has thickened, 4-7 minutes. Remove the pan from the heat.
Place the salmon on a parchment paper-lined baking sheet and cover each fillet with the sauce.
Bake for 12-15 minutes, depending on your desired doneness.
Serve the salmon the pineapple bowls over rice with more pineapple sweet chili sauce on the side.