03Meanwhile, lightly prick sausages in a couple of places with tip of a sharp knife, then cook sausages in remaining 1/2 tablespoon oil in a 10-inch nonstick skillet over moderately high heat, turning occasionally, until golden brown and cooked through, 12 to 15 minutes. Transfer to a cutting board.
04Drain cooked lentils in a sieve set over a bowl and reserve cooking water. Stir lentils into vegetables with enough cooking water to moisten (1/4 to 1/2 cup) and cook over moderate heat until heated through. Stir in parsley, pepper, 1 tablespoon vinegar, and 1 tablespoon fennel fronds. Season with vinegar and salt.
05Cut sausages diagonally into 1/2-inch-thick slices. Serve lentils topped with sausage and sprinkled with remaining tablespoon fennel fronds. Drizzle all over with extra-virgin olive oil.