In a medium pot, bring onion, carrot, celery,
bay leaf, and lentils to a boil. Reduce to a
simmer and cook until lentils are tender, about
25 minutes. Drain. Season with salt and pepper.
Add olive oil and lemon juice. Stir in
arugula and cover to keep warm. Meanwhile,
heat oven to 375 degrees. Arrange fillets in a baking
dish. Drizzle with olive oil and season with salt
and pepper. Cover with foil and bake until
cooked through, about 16 to 18 minutes. Serve
with lentils and squeeze with lemon juice.