Special equipment: a candy thermometer
Line a small cookie sheet or quarter sheet pan with parchment paper. Spray lightly with nonstick spray.
Spray a large bowl. Add the almonds, pecans, dried pineapple, millet, oats and coconut flake and stir well.
In a medium saucepot fitted with a candy thermometer, add the brown sugar, maple syrup, pineapple juice concentrate and salt; mix together with a heatproof spatula. Place the pot over high heat and cook the syrup to the soft-ball stage (240 degrees F), about 10 minutes.
Pour the syrup over the nut mixture and toss well. Scrape onto the prepared cookie sheet and press firmly and evenly into a tight, compact layer. Cool for about 20 minutes in the refrigerator.
Transfer to a cutting board and cut into 16 to 20 bars. Store in an airtight container.