In a large pot, warm the oil over medium-high heat. Being careful to stand back as the oil will likely splatter, add the cumin and mustard seeds and allow to cook until they start to crackle and change color, for 10-15 seconds.Add the diced onion, jalapenos, fresh ginger, and garlic along with the turmeric, coriander, cayenne and salt then stir together. Pour in the drained diced tomatoes and continue to cook over medium-high heat until they start to break down, for about 10 minutes. Mash them with the back of a spoon until they are macerated.Stir in the presoaked split peas with 3 and 1/2 cups water then bring to a boil. Reduce to a low boil and allow to cook until the peas are soft enough to mash, for about 30 minutes. This may take longer depending on how old the peas are. Add more hot water as needed until they are thoroughly cooked. Use a spoon or a whisk to mash the peas.Add the spinach to the pot and cook until it starts to wilt, for about 5 minutes. Serve warm with whole grain naan, brown basmati rice, and fresh cilantro then enjoy!