Paneer Sandwich

Cut the paneer into small cubes and place them in warm water while you prepare the rest. This keeps refrigerated paneer tender.
Blend the cilantro, mint, green chili, lemon juice, salt, and enough water to make a smooth, thick, spreadable chutney. Set aside.
Toss the sliced red onion with lemon juice, Kashmiri chili powder, and salt. Set aside for 5 to 10 minutes.
Heat the oil in a skillet over medium heat. Add the onion and bell pepper and cook until softened. Add the ginger, garlic, and tomato and cook until the tomato softens. Stir in the garam masala, Kashmiri chili powder, turmeric, ketchup, and salt.
Drain the paneer and add it to the skillet. Toss gently until the cubes are evenly coated with the masala. Cook for 2 to 3 minutes. The filling should be fairly dry, not saucy. Stir in the cilantro, remove from the heat, and let it cool slightly.
Spread green chutney inside each bread slice. Divide the paneer filling between 4 slices. Top each with lacha onion and shredded mozzarella. Close with the remaining slices.
Spread softened butter over the outside of each sandwich. Heat a skillet over medium-low to medium heat and toast the sandwiches until golden and crisp on both sides and the cheese has melted, turning once.
Cut each sandwich diagonally in half and serve hot with extra green chutney and lacha onion.