Yes. For the best flavor, first, sauté the vegetables in a little olive oil. Otherwise, add the vegetables and stock to your slow cooker and cook on HIGH for 2-3 hours or LOW for 6-8 hours (or until the rice is tender), adding the chicken in the last 30 minutes and the lemon right before serving. Note, slow cooker chicken and rice soup will yield mushier rice (to avoid this, you could use rice you’ve cooked separately and add it in at the end just to warm it up). Avoid short-grain rice. If you have a leftover chicken carcass (from a roast), you could also add that to the slow cooker.