Preheat the oven to 180oC (350oF).
Cut off the top and tail of the runner beans. Roughly chop them into pieces a few centimetres long.
Add the onion, garlic cloves and ginger to the jug of a Vitamix blender. Blend until finely minced. Add the runner beans and pulse until quite finely chopped.
Heat the oil in a large frying pan over a medium heat. Add the runner bean mixture from the blender jug along with the grated potato. Cook for 15 minutes over a medium-low heat, stirring often, until the potato and onion are softened. Stir in the garam masala, cumin and lemon juice. Season with salt, to taste.
Cut the sheets of filo pastry in half lengthways so you end up with tall strips a few centimetres wide. Keep the filo pastry covered with a damp cloth whilst you work.
Working with one sheet of pastry, take a tablespoon of the filling and place onto the bottom of the sheet. Grab the bottom left corner and pull up and over the filling to form a triangle. Grab the bottom left corner of the triangle and pull up and to the right to fold the triangle over. Repeat until you reach the top of the piece of filo. Place the triangle onto a baking sheet which has been brushed with olive oil. (See the GIF in the post for how to shape them if you're confused).
Repeat with the remaining filo and filling. Once all the triangles are formed, brush with some olive oil and sprinkle on sesame seeds. Bake for 10-15 minutes until golden brown. Eat warm with the chutney.