Cook Lentils to Tender Perfection: Rinse lentils thoroughly under cold water. In a medium saucepan, combine lentils with 4 cups of water, garlic cloves, bay leaf, and half of the kosher salt. Bring to a rolling boil over medium-high heat. Lower the heat to a gentle simmer and cook uncovered for about 20 to 30 minutes, or until the lentils are tender but not mushy. Drain off any remaining water and discard the bay leaf and garlic cloves.
Prepare and Season Vegetables: Preheat your oven to 425°F (220°C). On a large rimmed baking sheet, spread out the halved Brussels sprouts, cubed butternut squash, and chopped red onion. Add the fresh thyme sprigs. Drizzle the vegetables with olive oil, then sprinkle coriander, paprika, the remaining kosher salt, and cracked black pepper evenly over them. Toss everything gently to ensure all pieces are coated with oil and spices.
Roast Vegetables Until Caramelized: Place the baking sheet in the preheated oven and roast the vegetables for approximately 40 minutes. Toss or stir the vegetables halfway through roasting to promote even cooking and browning. Once roasted, remove the thyme sprigs and discard them.
Whisk Together the Maple-Mustard Dressing: In a small mixing bowl or glass jar, combine apple cider vinegar, maple syrup, and Dijon mustard. Slowly drizzle in the olive oil while whisking continuously to create a smooth, emulsified dressing. Season with salt and pepper, adjusting to your taste preference.
Combine Salad Components and Serve: In a large bowl, mix together the cooked lentils and roasted vegetables. Pour in half of the dressing and toss gently to coat the salad evenly. Transfer to a serving platter or bowl, drizzle the remaining dressing over the top, and sprinkle with crumbled goat cheese and toasted pumpkin seeds if using. Serve warm, at room temperature, or chilled.