Take thick, fresh curd in a mixing bowl. If too watery, hang in muslin cloth for 15-20 minutes to remove excess whey.
Add salt, black pepper powder, roasted cumin powder, and chaat masala to the curd. Mix well and adjust seasoning to taste.
Finely chop all vegetables—cucumber, tomato, onion, green bell pepper, coriander leaves, and green chili. Deseed tomato and cucumber, then pat dry with paper towel.
Add all chopped vegetables to the spiced curd mixture. Mix gently but thoroughly until vegetables are well coated.
Trim bread edges if desired. Lightly toast for crunch if preferred, or use as is. Spread thin layer of butter if using.
Place 4 bread slices on clean surface. Spread generous amount of curd-vegetable mixture on each slice, leaving small border. Top with remaining bread slices.
Cut each sandwich diagonally into triangles or rectangles. Serve immediately or wrap tightly for later. Enjoy!
Notes
Use thick, hung curd to prevent soggy sandwiches. Deseed vegetables to remove excess moisture. Best served fresh, but can be wrapped and stored for 2-3 hours if needed.