Place all of the paste ingredients into a mini food processor fitted with an S-blade (Note 1). Blend until relatively smooth, stopping to scrape down the inside of the bowl as needed.
Coat the bottom of a large pot with 1 tablespoon of the oil and place it over medium heat. Give the oil a minute to heat up, then add the tofu cubes in a single layer. Cook the tofu for about 10 minutes, flipping the pieces once or twice, until golden brown. Transfer the tofu to a plate.
Add the remaining tablespoon of oil to the pot, then add the cumin and mustard seeds. Cook the seeds for about 1 minute, stirring constantly.
Add the paste to the pot and cook it with the seeds for about 1 minute, stirring constantly, until it thickens and darkens slightly.
Stir in the water, potatoes, green beans, and pepper. Raise the heat to high and bring the liquid to a boil, then reduce the heat to a low simmer, cover the pot, and let the mixture cook for about 25 minutes, until the potatoes are fork-tender. Uncover the pot and stir the mixture every 5 to 10 minutes while it cooks. Replace the lid after stirring.
Uncover the pot and stir in the tomato sauce and tofu. Let the mixture simmer for 5 minutes longer, until the sauce thickens slightly.
Remove the pot from heat and stir in the vinegar and brown sugar. Season the mixture with salt to taste, then add cayenne pepper to taste.
Serve with rice and top each portion with a sprinkle of fresh cilantro.