Heat 1/2 tsp of oil in a saucepan and add the peanuts and sesame seeds. Toast them until they just begin to change color, remove to a plate to cool, and add the coconut to the saucepan.
Roast the coconut until it turns very lightly golden. Coconut burns very fast, so don't walk away from it and stir constantly.
Place the sesame seeds, peanuts and coconut in a blender along with the tamarind (make sure there are no seeds) and process with some water to a very smooth paste.
Heat the remaining oil. Add the cardamom, cloves and cinnamon and saute until they just start to brown and become fragrant. Add the cumin and mustard seeds and when they sputter, add the onions.
Saute the onions for a few minutes or until they start to brown at the edges. Then add the sliced peppers and stir fry until they start to brown slightly.
Add the turmeric, chili powder, coriander powder and cumin powder and stir until they are evenly distributed and roasted, about a minute or two.
Add the peanut-coconut-sesame paste and mix it well. Add some water if the sauce is too thick. Bring the sauce to a boil, then lower the heat to a simmer and cook until the peppers are tender but still have a bite to them.
Stir in the lemon juice, garnish with coriander, and serve hot with the Peshawari Naan (recipe follows).