Chop the onions and fry them in a large pot with a little olive oil.
When the onions become translucent, add the tomato sauce, turmeric (and possibly the other spices), mix well and leave to fry for 2/3 minutes over low heat.
Rinse the split peas and add them to the pot.
Cover with water (up to 1 cm above the ingredients).
Pierce the lemons with a pick to make several small holes and add them to the mixture.
Cover and cook over low heat for about 40 minutes.
While the split peas are cooking, prepare the potatoes. Rinse them and cut them into medium-sized sticks. Place them in an ovenproof dish, drizzle with olive oil, season with salt and pepper and bake at 200°C for 35/40 minutes. Stir 2 or 3 times during cooking.
Check from time to time if it is necessary to add water as well as the split peas cooking and mix. The split peas should remain a bit firm, but as they can take a long time to cook, don't hesitate to taste. If they start to fall apart, they are overcooked.
After about 40 minutes, infuse the saffron in a little hot water for 3 minutes and add the saffron water to the mixture.
Cook for another 10 minutes, add salt and pepper and taste to adjust the seasoning and cooking.
Just before serving, place the French fries on top.