Heat the oil in a heavy 5-quart pot over medium-high heat.
Add the onion along with about 1/2 teaspoon of the salt and cook, stirring occasionally, until softened, about 5 minutes.
Add the garlic, ginger, cumin, coriander, paprika, and turmeric and cook, stirring constantly, for 60 seconds.
Add the split peas, the remaining salt, pepper, and water. Give it all a good stir.
Raise the heat to high and bring to a boil.
Reduce the heat to maintain a simmer and cover the pot.
Cook, stirring occasionally, until split peas are very tender and most have lost their defined shape, about an hour.
Stir in lemon juice and cilantro.