Preheat the oven to 350°F. Coat a 9x13-inch glass baking dish with nonstick cooking spray.

Heat the olive oil in a deep skillet over medium heat. Add the sliced zucchini and cook, stirring often, until softened, about 5 minutes. Alternatively, blanch the zucchini in boiling salted water for 3 to 5 minutes and drain well.

In a separate large skillet, brown the ground beef over medium-high heat. Drain off any excess fat, then add the diced onion and cook until translucent, about 3 to 4 minutes.

In a large bowl, toss the melted butter with the stuffing mix until evenly moistened. Spread half of the stuffing mixture (about one box's worth) evenly over the bottom of the prepared baking dish.

In a large mixing bowl, stir together both cans of undiluted condensed soups, the sour cream, and the shredded carrots until well combined.

Fold the drained cooked zucchini into the soup mixture.

Add the cooked ground beef and onions to the bowl and stir everything together. Spoon the filling over the stuffing layer in the dish, taking care not to disturb the stuffing underneath.

Sprinkle the shredded Italian cheese blend evenly over the meat and zucchini mixture.

Sprinkle the remaining buttered stuffing mix evenly over the top.

Bake uncovered for 30 minutes, until the stuffing is golden brown and the casserole is hot and bubbling throughout.