Stir together the red onion, cilantro, bell pepper, chaat masala if you’re using it, and salt in a small bowl, taste, add more salt or chaat masala if necessary, and set aside.
Preheat a nonstick or cast-iron griddle over medium heat for a full minute before greasing it with a film of oil. Pour 1/4 cup of the batter onto the griddle. Uttapam are usually 5- or 6-inch pancakes 1/4 to 1/2 inch thick; if the batter is particularly thick or cold, you may need to spread it with the back of a spoon (or the measuring cup) to those dimensions.
After a minute or so, scatter the top of the pancake with a couple tablespoons of the onion-cilantro-pepper mix. When the bottom starts to color and crisp, 2 to 3 minutes later, flip the pancake and cook for another 4 to 5 minutes, until the second side is crisped and colored. Serve hot.
