1 onion, chopped
1/4 cup olive oil
2 carrots, diced
2 stalks celery, chopped
2 cloves garlic, minced
1 teaspoon dried oregano
1 bay leaf
1 teaspoon dried basil
1 (14.5 ounce) can crushed tomatoes
2 cups dry lentils
8 cups water
1/2 cup spinach, rinsed and thinly sliced
2 tablespoons vinegar
salt to taste
ground black pepper to taste