1. Start by combining the marinade ingredients: 2 tablespoons oil, 2 cloves garlic (minced), ½ tablespoon ginger (minced), ½ teaspoon salt, ½ teaspoon turmeric, and ½ teaspoon ground cumin) in a shallow dish. Mix well to create a sticky marinade. Place the 4 salmon fillets in the dish, turning them to coat thoroughly in the marinade. Let them sit while you prepare the daal, or refrigerate for up to 12 hours if you want to make this dish ahead of time.
2. Heat a heavy-based saucepan over medium-high heat and add 1 tablespoon oil. Once hot, add the 1 medium onion (finely chopped) and sauté until softened and translucent, about 5 to 7 minutes. Stir occasionally to prevent burning.
3. Lower the heat to low, then add 6 cloves garlic (minced), 1 tablespoon ginger (minced), and the 8 fresh curry leaves. Cook for about 30 seconds, stirring constantly, until fragrant. Be careful not to let the garlic burn, as it can become bitter.
4. Add the 1 cup dried split red lentils to the saucepan. Stir to coat the lentils with the aromatic mixture. Next, pour in the 3½ cups broth and add ¾ teaspoon salt, ½ teaspoon ground cumin, ½ teaspoon turmeric powder, ¼ teaspoon ground fennel, and ¼ teaspoon ground coriander. Mix well to combine.
5. Bring the pan to a simmer without covering it. Once simmering, reduce the heat to low and cover the pan with a lid. Let it cook for about 35 minutes, stirring every few minutes. The lentils will begin to break down into a thick daal.
6. After approximately 45 minutes, check the consistency of the daal. It should be thick and creamy, with the lentils fully broken down. Stir in ¼ teaspoon garam masala and adjust seasoning with more salt if necessary.
7. While the daal is simmering, prepare the salmon. Heat a large skillet over medium heat and place the marinated salmon fillets presentation side down. Cook for about 3 minutes, then carefully flip them and cook for another 3 minutes, or until the salmon is just cooked through and flakes easily with a fork.
8. Remove the cooked salmon from the pan and place it directly on top of the daal. Cover to keep warm while you prepare the final touches.
9. Add the remaining 2 tablespoons oil to the same skillet. Once hot, add the 1 small onion (cut into half moons) and sauté until softened and golden, around 5 minutes. Increase the heat until the onions begin to sizzle and caramelize.
10. Remove the pan from the heat, then add 1 teaspoon black mustard seeds, 1 teaspoon cumin seeds, and an additional 6-10 fresh curry leaves. Let it sizzle for about 20 seconds, then pour this tempering over the salmon and daal just before serving. Enjoy your Salmon Daal warm!