Combine first 6 ingredients in a food processor, and pulse until a smooth paste forms, stopping to scrape down sides. Set aside.
Cut 4 (12- x 12-inch) pieces of heavy-duty aluminum foil. Place 1 halibut steak in center of each; spread each steak with 1 tablespoon cilantro mixture. Top steaks evenly with lemon slices. Fold foil to seal.
Place foil packets on a baking sheet. Bake at 400º for 15 minutes or until fish flakes easily with a fork.
Serve Saison-style beers from Belgium (such as Saison Dupont) or the similar French bière de garde style (such as Jenlain from Brasserie Duyck). Their earthy, herbal qualities marry nicely with the cilantro and mint.