Prep ingredients: Finely grate 1⁄4 tsp of lemon zest, then squeeze 2 tsp lemon juice, keeping them separate. Peel and finely chop 1 large garlic clove. Coarsely chop baby kale. Pick 1 tsp whole parsley leaves from stems, and reserve for step 6. Finely chop remaining parsley leaves and stems.
Cook rice: Rinse rice in a mesh sieve until water runs clear. Heat 2 tsp of oil in a small saucepan over medium heat. Add rice, cook until fragrant, 1 minute. Add 1 1⁄4 cups water and 1⁄2 teaspoon salt and bring to a boil. Cover and cook over low until rice is done, about 17 minutes. Add spinach and chopped parsley to saucepan. Remove from heat and cover.
Season chicken: Pat chicken dry, then season all over with 1 tablespoon flour, 1⁄2 teaspoon salt, and a few grinds pepper.
Brown chicken: Heat 1 1⁄2 tsp of oil in a large skillet over high. Transfer chicken to skillet, then reduce heat to medium-high. Cook until golden brown on both sides, 3–4 minutes. Transfer chicken to a plate.
Making the sauce: Add lemon zest, garlic, and 1 tablespoon oil to the skillet. Cook until fragrant. Whisk in lemon juice, and 1 ½ cup of chicken broth. Return chicken thighs and juices to skillet. Bring liquid to a boil, then cover. Reduce heat to medium; braise until chicken is cooked through, about 5 minutes. Transfer chicken to a plate.
Finish sauce & serve: Bring liquid in skillet back to a boil, then sprinkle in 1 teaspoon flour, whisking constantly. Cook until sauce is thick 1–2 minutes. Return chicken to skillet, turning to coat in sauce. Stir baby kale and parsley into rice. Garnish with remaining whole parsley.