In a large saucepan or deep skillet, melt 3 tablespoons of the
butter over medium-high heat. Add the olive oil and the
onion and cook for 3 to 4 minutes, until onion begins to
soften. Add the mushrooms and cook,
stirring, for 3 to 4 minutes, until mushrooms begin to
brown. Add the remaining tablespoon of butter and the
zucchini and cook, tossing the vegetables every minute or
so until the zucchini is cooked through, about 6 minutes.
Add the corn and toss until the corn is heated through.
Remove from the heat, add the dill and salt and pepper to
taste, and toss. Serve immediately.