Prepare the following, adding each to the same medium bowl as you complete it: Thinly slice 6 ounces cremini mushrooms (about 2 cups). Dice 1 medium yellow onion (about 1 cup). Mince 2 garlic cloves. Peel and mince a (1-inch) piece of ginger (about 1 tablespoon).
Cut 1 ½ pounds boneless chicken thighs into 1-inch pieces. Season all over with ½ teaspoon of the kosher salt and ¼ teaspoon black pepper.
Place 1 cup of the low-sodium chicken broth and ¼ cup red miso paste in a liquid measuring cup or small bowl and whisk until the miso is dissolved.
Heat 2 tablespoons unsalted butter and 1 tablespoon toasted sesame oil in a large, high-sided skillet or Dutch oven over medium heat until melted and shimmering. Add the mushroom mixture and remaining ½ teaspoon kosher salt. Cook, stirring occasionally, until softened and the mushrooms have released their liquid and the liquid is almost evaporated, about 8 minutes.
Add 1 ½ cups jasmine rice and cook, stirring occasionally, until lightly toasted and fragrant, about 1 minute. Add the miso mixture and stir to combine with a wooden spoon, scraping the bottom of the pan to release any browned bits.
Add the remaining 2 cups chicken broth and the chicken, and stir to combine. Bring to a boil over medium heat, stirring occasionally so that the rice doesn't stick to the pot. Reduce the heat to low and cover. Simmer, stirring occasionally, until the chicken is cooked through, the rice is tender, and most of the liquid is absorbed, about 15 minutes.
Remove from the heat and stir in 1 cup frozen peas. Garnish with chopped fresh cilantro leaves and tender stems.
