Step 1

In 5-quart Dutch oven, melt 2 tablespoons of the butter over medium-high heat. Add chicken; cook 5 to 7 minutes without moving, until browned on first side. Stir; cook 2 to 4 minutes longer, stirring frequently, until chicken is no longer pink in center. Using slotted spoon, transfer to medium bowl; set aside.

Step 2

Add remaining 2 tablespoons butter to Dutch oven; stir in mushrooms, bell pepper and green onion whites. Cook over medium-high heat 5 to 7 minutes, stirring frequently, until softened. Stir in garlic and gingerroot; cook 30 seconds longer.

Step 3

Stir in broth, carrots, miso paste and soy sauce. Heat to boiling over high heat. Stir in chicken and noodles; return to simmering, then reduce heat and simmer uncovered 11 to 13 minutes, stirring frequently, until noodles are cooked through and sauce is thickened. Stir in spinach until wilted; stir in vinegar. Top with green onion greens.