Toss the oats with the butter on a rimmed baking sheet and spread in an even layer. Bake until toasted, 18 to 20 minutes. Let cool completely, then transfer to a large bowl. Stir in the cashews, macadamia nuts, and coconut.
For the bars: Line a 9-by-13-inch baking pan with foil, leaving an overhang. Coat the foil with cooking spray.
Combine the sugar, butter, honey, salt and vanilla in a medium saucepan. Bring to a boil over medium heat, stirring occasionally; the mixture will bubble and foam. Boil for 30 seconds, then pour over the oat mixture and stir. Let cool slightly, then stir in the ginger, mango and pineapple. Pour the mixture into the prepared pan and press firmly with a rubber spatula to spread in an even layer.
Let the bars stand at room temperature until completely cool and firm enough to slice, 1 to 3 hours. Lift out of the pan using the foil overhang and cut into 20 bars. Store in an airtight container at room temperature for up to 5 days.
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