Place the salmon fillets in the slow cooker, skin side down.
In a small bowl, whisk together the honey, soy sauce, minced garlic, rice vinegar, and sriracha (if using). Pour this mixture over the salmon fillets, ensuring they are well coated.
Cover the slow cooker and set it to low. Cook for 2 to 3 hours, or until the salmon flakes easily with a fork.
In the last 30 minutes of cooking, mix cornstarch and water in a small bowl to create a slurry. Stir this into the sauce in the slow cooker to thicken it slightly.
Once the salmon is cooked, carefully remove it from the slow cooker and place it on a serving platter. Drizzle the thickened sauce over the salmon.
Garnish with sesame seeds and sliced green onions before serving.