Red Lentil and Spinach Dahl

Name: Red Lentil and Spinach Dahl
Prep time: 10 min
Cook time: 30 min
Total time: 40 min
Cuisine: Asian, Indian, African
Ingredients: 1 cup dried red split lentils; 2 cups vegetable stock; 1 cup water; 1½ Tbsp oil; ½ tsp cumin seeds; ½ tsp mustard seeds; 1 brown onion; 3 cloves of garlic; 1 thumb-sized piece of fresh ginger; 1 tsp turmeric; 1 400g tin of tomatoes; 4 big handfuls of fresh baby spinach; ½ tsp chilli flakes*; ½ medium or 1 small lemon; Salt, to taste