Sift the matcha through a fine-mesh sieve into a 12 cm / 5-inch bowl. Add the 60 ml of warm water (70 C / 160 F) and whisk for about 30 seconds until no lumps remain and the surface is frothy.
In a 1.5-liter / 6-cup mixing bowl, combine the shaken coconut milk, 190 ml cold water, maple syrup, vanilla, lemon juice and salt. Pour in the matcha mixture and whisk until evenly green, then add the chia seeds and whisk for 1 full minute so the seeds separate.
Let the bowl sit on the counter for 10 minutes. Whisk again, scraping the bottom, until you see no clumps and the mixture looks slightly thickened.
Divide the mixture among four 200 ml / 7 oz jars, about 140 ml each. Cover and chill for at least 4 hours, or overnight, until the gel holds a spoon trail.
Dice the mango. Just before eating, top each jar with a quarter of the mango and a half tablespoon of coconut flakes.