In large saucepan, bring water and salt to a boil over high heat. Gradually stir in grits; reduce heat and simmer gently, stirring frequently to prevent sticking until mixture is very thick (about 30 min.). Stir in butter and Parmesan; spoon mixture into a foil-lined, oiled 8x4x2" loaf pan and let set for 10 min. Invert onto cutting board; cut into 8 slices. In large skillet, add enough olive oil to lightly cover the bottom of the pan; heat for 3 min. over medium heat. Add polenta slices to pan. Sauté until light golden-brown (about 3 min./side), turning once; set aside, covered. Heat additional olive oil, if necessary; season fish with salt and pepper. Place fish in pan; press lightly with spatula to keep it from curling up. Cook fish 4 min.; turn and continue cooking until fish is opaque (4-6 min.).
To Serve: Place 2 polenta slices on each of 4 dinner plates; arrange each fillet partially over polenta. Top fillets with Mexican Shrimp Cocktail; garnish with cilantro. Serve immediately.