Preheat oven to 400°F. Cut up any large broccoli or cauliflower florets into bite-size pieces. Set aside.
Melt butter in large skillet on medium heat. Add onion; cook and stir about 5 minutes or until tender. Stir in flour, Italian seasoning, garlic salt and pepper. Add milk; cook and stir until thickened and bubbly. Add cream cheese and Parmesan cheese; cook and stir until cream cheese is melted. Add vegetables; toss gently to coat. Spoon into 2-quart baking dish. Sprinkle evenly with Cheddar cheese. Top with potato nuggets.
Bake 45 to 55 minutes or until heated through and potato nuggets are golden brown and crispy.