In a small pot, combine the lentils with 2 cups of water and bring them to a boil. Cover with a lid, simmer over medium heat until tender, 20 minutes. Drain well and let cool.
On a rimmed baking sheet, toss the cauliflower with the 1/4 cup of olive oil and the spices and salt. Roast for 15 minutes, flipping them halfway through until the cauliflower is tender and golden brown.
In a bowl, whisk the tahini with the lemon juice and 2 tablespoons of water until smooth.
Add most of the dressing to the lentils, season with 1 ½ teaspoon of salt, toss to coat.
Add the roasted cauliflower into the bowl along with onion, and spinach or arugula. Toss the salad, transfer to a platter, sprinkle with toasted almonds, and drizzle with remaining dressing.