In a small saucepan, bring water to a rolling boil. Stir in cornmeal and salt and reduce heat to low. Continue to simmer, stirring constantly, for 3 minutes - it will thicken considerably.
Remove from heat and stir in 1 cup cheese and Montreal Steak seasoning. Spread into the bottom of a greased 9 x 13 baking dish.
In a deep skillet, saute ground beef, onion, and zucchini until beef is brown and vegetables are tender. Drain and return to pan.
Stir in undrained tomatoes and tomato paste. Cook on low for 10 minutes.
Spread over polenta layer in baking dish. Bake at 350 for 25 minutes. Sprinkle remaining cheese on top and bake an additional 5 minutes, or until cheese is melted. Allow to cool slightly before serving.