Lentil and Sweet Potato Stew

olive oil

large onion (, chopped)

medium carrots (, peeled and chopped)

bay leaf

garlic clove (, minced)

vegetable broth or water

dried brown lentils

medium sweet potatoes (, peeled and cut into ½ -inch dice)

((14.5 ounce) fire roasted diced tomatoes in juice, undrained)

Salt and pepper

fresh cilantro (, chopped, optional)

Sour cream or plain low-fat yogurt for serving (, optional)