In a large stockpot, heat butter over medium heat.
Add in garlic, onions, carrots, and potatoes. Stirring often, cook for about 5 minutes.
Add in the chicken broth. Cover and cook for 15 minutes. The carrots and potatoes should be soft.
Add in corn, zucchini, tomatoes, chicken and/or ham, and seasonings (not the cornstarch.)
Heat for another 10-15 minutes, until mixture is starting to boil.
Lower heat and add all but 2-3 tablespoons of the evaporated milk.
Mix in remaining evaporated milk with the cornstarch and mix until combined. Stir this into the stew.
Let simmer for another 10 minutes.
Top with some shredded Parmesan cheese on top of each bowl of chowder.