Spicy, garlicky soba noodles and dark green kale yield a hearty and quick vegetarian meal. Leeks add a delicate, onion flavor. We liked using a buckwheat-wheat blended soba noodle, but any variety will work. The dish is fine as is, though a sunny-side up egg would be a nice complement. Gochujang, a chili paste common in Korean cooking, adds savory-salty heat to the noodles. It can be found in Asian markets and most larger supermarkets.