Pre-cook the yellow split peas by boiling them in a pot with water for 25-30 minutes, or until they are partially cooked, then drain them, reserving liquid.
Place garlic and onion into a large mortar and pestle and pound until almost a paste (if no mortar and pestle is available, finely chop both the garlic and the onion and place in a small bowl). Add crushed chili pepper and sliced fresh ginger (or finely chopped) and grind into a paste with garlic and onion.
Coat the bottom of a large pot with the vegetable oil and heat over medium heat. When oil is hot, add the contents of the mortar and pestle and sauté, stirring constantly, until onions and other ingredients are starting to brown. Add the cayenne powder, turmeric powder, cumin powder and tomato paste. Add the cubed goat meat and cook, stirring, until browned (partially cooked but not tender). Add the pre-cooked lentils and approximately ½ cup of the reserved cooking liquid, or enough to keep the meat covered. Add 1 teaspoon salt and 1 teaspoon fish sauce (or more of either to taste). Cover the pot and cook the meat until tender, stirring occasionally, at a slow boil, for approximately an hour. Add more reserved cooking water to keep meat covered while cooking. Adjust seasoning and spiciness to your taste.
Serve goat curry over cooked basmati rice, garnished with chopped cilantro.