Make the Peanut Chutney: Combine all the ingredients with 3 tablespoons water in a blender and blend on low speed, occasionally using a spoon or small spatula to scrape down the sides, until mixture resembles a chunky paste. If mixture isn't blending properly, add a little more water, a few drops at a time, to get it going. Taste and adjust salt, if needed. (This chutney keeps, refrigerated in an airtight container, for up to 1 week.)

Make the Pesarattu: Drain and rinse mung beans, then transfer them to a blender and add ginger, salt, green chile, and 1 cup water. Blend until mixture forms a pasty batter, with tiny flecks of mung bean visible. Transfer batter to a bowl.

In a large non-stick skillet over medium-high heat, warm 2 teaspoons of the oil. Once oil begins to shimmer, pour ⅓ cup of the batter into the skillet, spreading it out with the back of a large spoon to make a thin, 7- to 8-inch pancake. Sprinkle a few curry leaf pieces and 2 teaspoons of the onion (or more, if you really like onions) over the top of the pancake. Reduce heat to medium and cook pancake until edges are slightly crisp and browned, 2 to 4 minutes. Flip pancake and cook for 2 to 4 minutes more, until onion on the underside is brown. Flip pancake one more time and cook for another minute if you want edges to be extra crispy. Sprinkle finished pancake with a little salt, then transfer to a plate. Repeat with remaining batter, curry leaves, and onion, adding 2 teaspoons oil to pan between each batch. Serve pancakes with peanut chutney.