Place the broccoli in the bowl of a food processor, and pulse until very very finely chopped (about the size of a grain of rice). Set aside.

Heat the oil in a large stockpot over medium-low heat. Add the cumin and mustard seeds, and stir for 1 minute. Increase heat to medium, and add the onion. Cook, stirring occasionally, until the onion softens. Stir in the chopped broccoli, broth, coconut milk, lentils, 1/2 teaspoon of salt, garam masala, turmeric, and crushed red pepper. Increase heat to high and bring to a boil. Stir, cover, and reduce heat to a simmer. Simmer, stirring occasionally, for 10 minutes. Remove lid and simmer for another 10 minutes, stirring occasionally, until the lentils are tender and the liquid has reduced a little. Stir in the lemon juice. Taste, and add more salt, pepper, or lemon juice as needed. 

Serve hot, with naan or pita, and wedges of lemon.