Fine beans and potato curry

Potato curry

• 200g of fine beans, cut into 1cm long pieces
• 3 large white potatoes, diced into 1cm cubes
• 10g of ginger
• 2 garlic cloves
• 2 tbsp of vegetable oil
• 1 tsp cumin seeds
• 1/2 tsp turmeric powder
• 1/2 tsp red chilli powder
• 1 large ripe tomato, finely chopped
• 1 tsp tomato paste, optional
• 1/2 tsp garam masala, optional
• 1/2 lime, for juice only
• salt