In a large bowl, cover the dried green split peas with 4 cups of water and let soak overnight.
Chop one of the onions and thinly slice the other. Seed and slice the Anaheim chili and the jalapeno. Slice the garlic. Peel and coarsely chop the tomato.
Drain and rinse the split peas and transfer them to a food processor. Add the chopped onion, Anaheim chile, 1 tsp ginger, salt, and 1/4 cup of water, and process until pureed. Set aside while preparing the spinach.
To prepare the spinach, heat the 2 T vegetable oil in a large saucepan. Stir in the mustard seeds and the cumin seeds and cook over moderately high heat, stirring, for 1 minute. Add the turmeric and the garam masala and cook for 1 more minute.
Add the sliced onion and the 1 tsp ginger and cook, stirring, until the onion is softened, about 3 minutes. Stir in the sliced garlic and jalapeno and continue cooking until fragrant, about 2 more minutes.
Add the fresh spinach to the pan in large handfuls, stirring until the leaves are wilted before adding another handful. Cook, stirring, until the exuded liquid has evaporated, about 2 minutes. Stir in the butter until melted, then add the chopped tomatoes. Lower the heat to moderate and simmer, stirring occasionally, until the mixture is thickened, about 10 minutes. Season the mixture with salt and pepper and keep warm.
To make the pea cakes, heat the 3/4 cup vegetable oil in a large skillet. For each cake, drop 2 tablespoons of the split pea mixture into the skillet, pressing down on them lightly to make 3-inch rounds. Fry the cakes over moderately high heat until browned on the bottom, about 4 minutes. Turn the cakes and brown the other side, 2 to 3 minutes longer. Transfer to paper towels to drain and keep warm while you fry the remaining cakes.
Arrange the green pea cakes on 4 large plates and spoon the gingered spinach alongside. Garnish the dish with the fresh cilantro leaves and serve with lemon wedges.