Preheat oven to 375°F. Melt butter in a 12-inch heavy deep-sided skillet over medium heat. Remove from heat and stir in milk, stock, and polenta. Stir in corn, zucchini, scallions, parmesan cheese, 1 1/2 teaspoons salt, and 1/4 teaspoon pepper.
Bake 20 minutes; remove from oven and stir in tomatoes. Bake until polenta is tender and thickened, another 15 to 20 minutes; adjust seasoning, if needed. Stir in herbs and goat cheese. Serve sprinkled with more herbs and parmesan cheese.