Soba Soup with Spinach

INGREDIENTS

• 2 tablespoons vegetable oil
• 12 ounces shiitake mushrooms (stems removed), caps thinly sliced
• 4 scallions, white and green parts separated and thinly sliced
• 1 garlic clove, minced
• 1 tablespoon peeled and minced fresh ginger
• Coarse salt
• 2 cans (14.5 ounces each) reduced-sodium chicken broth
• 1/2 package (4.4 ounces) soba (Japanese buckwheat noodles)
• 1 bunch flat-leaf spinach, torn
• 2 tablespoons fresh lime juice
• 1 tablespoon soy sauce