Marie's Lentil Soup

INGREDIENTS

• 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