For the neatest granola bars, make sure they're thoroughly chilled before slicing, Use a serrated bread knife and a gently sawing motion to cut them into bars. Once the bars are cut, they can be stored at room temperature.
Heat oven to 350ºF. Line a 9x9 baking pan with parchment paper, letting the paper hang over the sides slightly.
Pour the oats and millet onto a rimmed baking sheet. Spread evenly and bake 8-10 minutes, or until lightly toasted. Remove from the oven and stir in the coconut, chia seeds, tea, lemon zest, and salt; mix well. Stir in half the chocolate chips.
Add the coconut oil, brown sugar, and honey to a saucepan set over medium heat. Cook, stirring frequently, 2-3 minutes, or until melted. Pour over the oat mixture and stir until everything is evenly coated.
Firmly press the granola into the prepared pan. Top with remaining white chocolate chips.
Chill until set, about 2 hours in the refrigerator or 30 minutes in the freezer. Lift from the pan and remove the paper. Use a serrated knife to cut into 12 bars.