Grind the coconut, one tablespoon chopped onion, coriander seeds, red chillies and tamarind pulp with a little water. Add garlic cloves and continue grinding to a fine paste.
Heat the oil in a deep non stick pan, add the remaining chopped onion and sauté till golden. Add the green peas, potato cubes, turmeric powder and stir well.
Add the coconut masala, two cups of water and salt and mix. Bring to a boil and then reduce heat and simmer for three to four minutes.
Adjust consistency. The gravy should not be too thick or too thin. Garnish with ginger and green chillies and serve hot.