Combine ingredients: Drain the soaked lentils and add to a rice cooker bowl. Thoroughly rinse the long-grain white rice and quinoa to avoid a gummy texture. Add to rice cooker bowl along with water (or vegetable broth). Optionally, you can add in olive oil and salt.
Start: Stir and set to cook on the "White Rice" or "Standard" setting.
Finish steaming: Don't open the rice cooker immediately once it finishes cooking. Allow it to keep steaming on the "Warm" setting for about 5 minutes to ensure everything is perfectly cooked.
Fluff: Use the rice paddle to gently fluff the rice and incorporate the quinoa and lentils.