Make the garlic chile oil: heat vegetable oil in a large saucepan over medium heat. Add garlic and cook, swirling pan often, until golden brown, 3 - 5 minutes. The garlic will continue to cook and darken slightly after it's off the heat. Transfer to a small bowl, leaving 1 tbsp of the oil in the pot. Stir red pepper flakes into the bowl and set aside
Add onion to the 1 tbsp of garlic oil still in the pot. Cook over medium heat until onion is translucent and beginning to take on some color, about 5 minutes
Pour in 8 cups of water, stir in rice, chicken thighs, and 1 tsp salt. Bring to a boil, then reduce heat to low and bring to a gentle simmer. Simmer uncovered until chicken is cooked through, about 20 minutes
Transfer chicken to a plate and let sit until cool enough to handle. Shred with two forks. Continue to simmer soup while prepping the rest of the ingredients
Strip kale leaves off center ribs and discard the ribs. Rinse kale thoroughly in cold water then thinly sliced the leaves crosswise
Add kale and shredded chicken to pot. Continue to simmer, stirring occasionally, until kale is bright green and chicken is warmed through, about 5 minutes
Remove pot from heat. Squeeze in lemon juice, season with 2 tsp salt and pepper to taste. Stir to combine
Divide among bowls. Drizzle with garlic chile oil and more black pepper