Steam the potatoes until they are very tender (15 to 20 minutes), and mash them thoroughly.

Steam the peas until they are tender (6 to 10 minutes if fresh; 3 to 5 minutes if thawed frozen).

Mash the peas thoroughly using a mortar and pestle or a food mill. You can also place the peas on a board and use a heavy object to mash them.

Combine the potatoes, peas, coriander, minced onion, sugar, salt, and red pepper in a large bowl.

Heat the oil in a large skillet over moderate heat until sizzling. Add the mustard seeds and sauté them until they start to pop.

Stir in the turmeric.

Add the potato-pea mixture, and cook for a few minutes, stirring often, to brown the potatoes lightly and to heat the mixture through.

Remove the mixture from heat, taste, and adjust the seasonings as needed.

Cut the pita bread into halves. Divide the potato mixture to fill the pockets, and insert the onion rings and alfalfa sprouts.