Put chickens thighs and buttermilk in a large bowl and cover for at least an hour (up to overnight). Remove from bowl and coat onion powder, red pepper flakes, smoked paprika, salt, and pepper.
Dice mangoes, garlic cloves, half of a red onion, and half bunch of cilantro. Set aside ½ of the diced mangoes.
Add olive oil to over medium heat. Allow heat to warm and add chicken thighs. Sear on both sides for about 4-5 minutes, until golden brown. Add red onions and garlic and saute until fragrant. Toss mangoes and cilantro together and add to pan. Cook until chicken thighs are finished, about 10 minutes. Allow chicken and juices to cool in a bowl.
Rinse rice thoroughly (4-5 rinses, until water is clear). Add 1 cup of rice and 2 cups of chicken broth to a rice cooker OR cook stovetop. When the rice is finished, add rice to and add coconut milk and sugar. Stir constantly until rice thickens. Remove from heat.
Add rice to a plate and add chicken, juices, and top with fresh mango set aside previously.