Step 1Heat the oven to 450 degrees. Peel and seed the squash and cut it into roughly three-fourths-inch dice. Line a jellyroll pan with aluminum foil and mound the squash in the center. Drizzle with 1 tablespoon olive oil, sprinkle with cumin, salt and pepper, mix well and arrange in a single layer. Roast until the squash is tender enough to be pierced with a sharp knife, about 15 minutes.
Step 2Place the lentils in a medium saucepan and cover with water by 2 inches. Season generously with salt and bring just to a boil. Reduce to a simmer and cook until the lentils are tender but firm, about 20 minutes. Drain, rinse well, stir in the vinegar and salt and pepper to taste.
Step 3While the lentils are cooking, heat 2 tablespoons olive oil in a large skillet over medium heat. Add the carrot, celery, onion and dried red pepper flakes, and cook until the onions and celery are translucent, about 5 minutes. Rinse the kale under water and add it, still dripping, to the skillet in heaping handfuls. Add the minced garlic and salt to taste, and stir to mix well.
Step 4Cover the pan, leaving the lid ajar, reduce the heat to low, and cook, stirring occasionally, until the kale is very soft, dark and frazzled looking, about 30 minutes. It should be very sweet.
Step 5Stir the lentils into the cooked kale, taste and adjust seasoning for salt, pepper and vinegar. Gently stir in about 2 cups of the roasted squash before serving.