In a small bowl, combine miso paste, ⅓ of the garlic, ⅓ of the ginger and 2 Tablespoons water; stir to thoroughly combine. Line a sheet pan with foil or parchment paper. Pat chicken breasts dry with paper towels; season with salt and pepper. Place on sheet pan and spread miso mixture on the top. Cook 20-22 minutes, or until browned and cooked through to an internal temperature of 165-degrees.
While chicken roasts, in a small pot, bring rice, a big pinch of salt and 1 1/4 cups water to a boil. Once boiling, cover and reduce heat to low. Simmer 15 minutes, or until the water has been absorbed and the rice is tender. Remove from heat and fluff with a fork.
Once chicken has roasted for 10 minutes, in a large pan, heat 2 teaspoons oil over medium-high heat. Add mushrooms and cook, stirring occasionally, 3-5 minutes, or until the mushrooms are lightly browned. Add the remaining garlic and ginger and cook, stirring occasionally, about 1 minute, or until softened and fragrant.
Add watercress, snow peas and sugar snap peas to mushrooms; season with salt and pepper. Cook, stirring frequently, 2-3 minutes, or until bright green.
Divide cooked rice and finished vegetables between four plates. Top with a chicken breast. Garnish with cashews. Enjoy!