Whisk together the coconut milk, ginger, lemon grass paste, lime zest, lime juice, salt and pepper in a large bowl.
Pour 1 cup of the marinade into a separate container, seal and refrigerate (this will be used later for the sauce).
Place the chicken in the bowl with the remaining marinade. Toss to coat and submerge the chicken in the mixture as much as possible.
Cover and marinade for at least 2 hours up to overnight.
Remove the chicken from the marinade, place on a baking sheet.
Heat the oven to 450 degrees and cook chicken for 20-25 minutes until golden brown and crispy.
While chicken cooks, pour the reserved marinade into a medium skillet over medium heat.
Whisk the cornstarch together with about 2 tablespoons of water until dissolved.
Add the cornstarch slurry to the skillet and whisk continuously until the mixture comes to a simmer and starts to the thicken. Once thickened, turn off heat and set aside.
For the Rice
Combine the rice, coconut milk and water in a small sauce pot.
Bring to a boil then reduce to low and cook covered until the liquid is fully absorbed by the rice.
Remove from the heat, add the chopped mango and stir to combine.
Serve the chicken with the rice and top with the sauce.