Preheat the oven to 425°F. Line two large rimmed baking sheets with parchment.

Remove the leaves from one head of cauliflower and trim the stem. Cut the cauliflower in half lengthwise and lay both sides flat on the cutting board. Cut the halves into ½-inch-thick pieces. Put the pieces on one lined baking sheet and toss with 2 tablespoons of the oil and ¼ teaspoon of the salt. Arrange in a single layer. Repeat with the other cauliflower and remaining oil and salt.

Roast, rotating and swapping the pans halfway through, until the cauliflower is browned, about 25 minutes. Remove from the oven and set aside.

Preheat a 4-quart pot over medium heat. Heat the oil, then sauté the onions with a pinch of salt until lightly brown, 5 to 7 minutes. Add the garlic and ginger and sauté for a minute more. Add the cilantro and stir until wilted.

Add the fennel seed, cumin, paprika, cardamom, and cayenne and stir to toast for about 30 seconds. Stir in the tomatoes, coconut milk, tomato paste, lime juice, and remaining 2 teaspoons salt. Cover and bring to a simmer. Once simmering, lower the heat and simmer for 10 minutes.

Preheat the oven to 375°F. Pour some sauce into a 9-by-13-inch casserole. Layer in half of the cauliflower and cover with half of the remaining sauce. Layer in the remaining cauliflower and pour on the remaining sauce. Bake for 20 minutes.

Remove from the oven, scatter the almonds and cilantro over the top, and serve.