Preheat oven to 400 F. On lightly greased baking sheet, place chicken and season with salt and pepper. Place in oven and heat for 25 minutes, or until chicken is cooked to an internal temperature of 165 F. When cool enough to handle, slice chicken.
In bowl, place miso, add 2 cups hot water, and stir well.
In heavy-bottomed saucepan, heat butter. Place mushrooms and carrot in pan and heat until softened, about 4 minutes. Add miso broth, peas, rosemary, and black pepper to pan; bring to a very gentle simmer and heat for 3 minutes. Dissolve cornstarch in 1/4 cup water and stir into pan; continue to heat until sauce has thickened. Stir in cooked chicken.
To serve, place toast slices on each of 4 plates and top evenly with chicken mixture.
Notes
Each serving contains: 368 calories; 32 g protein; 14 g total fat (5 g sat. fat); 30 g total carbohydrates (5 g sugars, 5 g fiber); 231 mg sodium