In a bowl, whisk together the eggs, milk, onion, salt, cumin, chili powder, red pepper flakes, turmeric, and cilantro or parsley until well mixed.
Pour the egg mixture into a wide, shallow container. Place the challah slices in the mixture, turning to coat both sides and allowing the bread to absorb the mixture fully.
Heat a large skillet over medium-low heat and add about 1 tablespoon of butter to the skillet. Allow butter to melt.
Place soaked bread slices in the skillet, leaving enough room between slices to flip. You will need to cook the French toast in batches. Cook over medium-low heat for 2–3 minutes per side, adding additional butter as needed, until golden brown and cooked through. Repeat with remaining slices.
Serve warm with butter. Serve with cilantro chutney or mango chutney for an additional savory twist.
