Coarsely grind the coriander, cumin, and mustard seeds in a spice grinder for 2–3 seconds. Alternatively, put them on a cutting board and press down on them with a heavy pot or pan to crush them.
Put the beans, tomatoes, coriander, cumin, mustard seeds, and turmeric in a large baking dish and stir until well combined.
Bake for 10 minutes.
Remove from the oven, stir, and bake for 10 minutes longer.