Combine the potatoes and peas with 3.5 cups of water in a saucepan and bring to a boil. Simmer over medium heat until the potatoes are fork-tender, about 10 minutes. Mash the vegetables directly in the water with a potato masher until broken down; the mixture should look liquidy but the vegetables should be completely softened.

Heat the butter in a large, wide pan over medium-high heat until shimmering. Add the cumin seeds and stir until they sizzle and smell fragrant.

Add the onion, bell pepper, and salt. Sauté until the vegetables are softened and starting to brown, about 10 to 15 minutes—if they start to stick, stir in a tablespoon of water to keep them moving.

Lower the heat to medium-low and stir in the garlic and ginger. Add the tomato paste and cook, stirring frequently, until the mixture is thick and darkened, about 3 minutes.

Stir in the coriander, garam masala, chat masala, smoked paprika, turmeric, red chili, and nutritional yeast. Pour in the mashed potato and pea mixture and stir to incorporate. Reduce the heat to low, cover, and simmer for about 5 minutes to let the spices permeate the vegetables until the consistency is a thick, scoopable gravy.

Slice the dinner rolls and toast them in a hot pan with butter or oil until the edges are golden and crisp. Serve the bhaji hot, garnished with raw red onion and cilantro, with plenty of lime to cut through the richness.