Place the dried lentils in a medium saucepan. Cover with cold water and allow the lentils to soak for one hour. Drain the lentils and return to the same saucepan.

Add 3 cups of water, the quartered onion, smashed garlic, bay leaf, and 3/4 teaspoon salt. Bring the lentils to a boil, reduce the heat to a simmer, and cook for 25 to 30 minutes, or until tender.

Drain in a fine-meshed sieve and discard the onion, garlic, and bay leaf. Place in a large serving bowl to cool. Toss with a tablespoon of olive oil.

Meanwhile, preheat the oven to 425°F. Slice the carrots into 1/2-inch rounds (the skinny ends can be left in larger chunks; keep the pieces as evenly sized as possible) and cut the radishes into quarters, reserving one radish for garnish.

Place the carrots and radishes on a large sheet pan with the skin-on garlic cloves and toss with 2 tablespoons of olive oil, 1 teaspoon salt, and 1/4 teaspoon freshly ground black pepper.

Roast for 20 to 30 minutes, tossing every 10 minutes or so, until the carrots and radishes are caramelized and tender. Squeeze the roasted garlic cloves out of their skins (discard the skins) and let the vegetables cool to room temperature.

Add the roasted vegetables and garlic to the cooked lentils along with the sliced red onion and toss gently to combine. Season to taste with salt and pepper.

In a small bowl, whisk together the tahini paste, lemon juice, salt, and pepper. It should be thick. Add 3 to 4 tablespoons of hot water (more or less depending on your brand of tahini) and whisk gently until smooth. The dressing should be the consistency of a thick salad dressing but still drizzle easily from a spoon.

Using a mandoline, cut the remaining radish into very thin slices. Roughly chop some of the reserved carrot tops (about 1/4 cup). Garnish the salad with the sliced radish and chopped carrot tops.

Drizzle the salad with the tahini dressing and serve at room temperature. This salad makes great leftovers and can be served cold from the fridge.