Put the lentils in a pot, along with the ba leaves and the baking soda. Cover generously with cold water, cover with a lid, and bring to the boil.
Once it's boiling, turn the heat down to the minimum, and let the lentils cook, covered, for about 20 minutes, until tender.
Drain the lentils in a fine sieve, and rince under cold water to stop the cooking process and cool the lentils down quickly. Discard the bay leaves. Let them drain while you prepare the rest of the ingredients.
Toast the cumin seeds in a hot dry pan over high heat for 1 or 2 minutes to develop the flavour of the spice.
Put the lentils in a large bowl with the lemon juice, toasted cumin seeds, pumpkin seeds, olive oil, piment d'Espelette (or other chili flakes), season with salt and pepper. Blend all the ingredients with a stick blender until getting a smooth hummus.