How to Make It
Coat a 5- to 6-quart slow cooker with cooking spray. Place the leeks in the slow cooker; toss with the thyme, sage, and 1/2 teaspoon of the salt and 1/4 teaspoon of the pepper, and spread in an even layer. Drizzle the leeks with the wine, and dot with the butter. Cover and cook on LOW until the leeks are tender, about 2 hours and 30 minutes.
Place the salmon on top of the leeks in the slow cooker. Sprinkle the salmon with the remaining 1/2 teaspoon salt and 1/4 teaspoon pepper; top with the lemon slices, and drizzle with the oil. Cover and cook on LOW until a thermometer inserted in thickest portion of the salmon registers 140°F, about 1 hour. Transfer the salmon to a platter, and serve with the leeks.