Moroccan lentil soup

• 1 tablespoon olive oil
• 2 onions, chopped
• 2 cloves garlic, minced
• 1 teaspoon grated root ginger
• 1.5L (2½ pints) water
• 200g (7 oz) red lentils
• 1 (400g) tin chickpeas, drained
• 1 (400g) tin cannellini beans
• 1 (400g) tin chopped tomatoes
• 3 carrots, diced
• 3 stalks celery, diced
• 1 teaspoon garam masala
• 1 1/2 teaspoons ground cardamom
• 1/2 teaspoon ground cayenne pepper
• 1/2 teaspoon ground cumin