In a large heatproof bowl, cover the lentils with the boiling water and let stand for 30 minutes. Drain.

In a large saucepan, heat 2 tablespoons of the olive oil. Add the diced carrots, onion, and celery and cook over moderate heat, stirring occasionally, until softened, about 8 minutes. Add the lentils and 1 1/2 cups of water and season with salt and pepper. Cover and cook over low heat until the lentils are just tender and the liquid is absorbed, about 20 minutes. Stir in 1/2 cup of the olive oil, the cider vinegar, and the roasted red peppers and season with salt and pepper. Transfer the lentil mixture to a serving platter.

In a large skillet, heat the remaining 2 tablespoons of olive oil. Add the merguez sausage and cook over moderate heat, turning occasionally, until browned and cooked through, about 8 minutes. Arrange the sausages around the lentils and pour over any accumulated juices.

Return the skillet to high heat. Add the pears and cook, turning once, until lightly browned, about 2 minutes. Transfer to the platter and serve right away.

The cooked lentils can be refrigerated overnight. Reheat gently before serving.