Split Pea Pancakes with Mushroom Relish

1 1/4 cups dried green split peas
8 3/4 cups water, divided
1/4 cup chopped fresh cilantro
1 Tablespoon grated peeled fresh ginger
1 Tablespoon grated unsweetened coconut
1 teaspoon cumin seeds
1 teaspoon kosher salt, divided
1 teaspoon ground turmeric, divided
1/2 cup plus 1 Tablespoon canola oil, divided
1 1/2 teaspoons mustard seeds
1 cup finely chopped red onion
1 serrano chili, minced
2 cups sliced shiitake mushroom caps (about 6 ounces)
1 cup chopped tomato
2 teaspoons sambal oelek (ground fresh chili paste)

1. Place peas in 8 cups water;  let stand for 2 hours.  Drain.  Place soaked peas, cilantro, ginger, coconut, cumin, 1/2 teaspoon salt, and 1/2 teaspoon turmeric in the bowl of a food processor.  Process until smooth.  With processor running, slowly drizzle in 1/2 cup water until a smooth batter forms. 
2. Heat a large non-stick skillet over medium high heat.  Add 1 Tablespoon oil and mustard seeds;  saute 3 minutes or until seeds begin to sizzle and smell pungent.  Add onion and serrano;  saute 3 minutes, or until tender.  Add mushrooms;  saute 6 minutes or until lightly browned.  Add remaining 1/4 cup water, tomato, sambal, remaining 1/2 teaspoon salt and remaining 1/2 teaspoon turmeric.  Simmer 5 minutes or until thickened.  Remove from pan;  wipe pan clean with paper towels.
3. Return pan to medium high heat; spoon 8 (1 1/2 Tablespoon) mounds of batter into pan;  flatten slightly to make pancakes.  Pour one-third of remaining 1/2 cup canola oil around cakes.  Cook 90 seconds on each side or until golden brown.  Repeat procedure twice with remaining batter and oil.  Top each pancake with 1 Tablespoon relish.