1Heat oven to 450ºF. In medium bowl, stir Bisquick mix, boiling water and onions until soft dough forms; beat vigorously 20 strokes.
2in ungreased 12-inch pizza pan, pat dough with floured hands, forming 1/2-inch rim.
3Bake about 10 minutes or until light brown. Cool 10 minutes.
4In medium bowl, stir cream cheese, sour cream, dill weed, garlic powder and tuna until smooth; spread evenly over crust. Refrigerate 1 to 2 hours or until chilled. Just before serving, top with vegetables and cheese. Cut into bite-size wedges. Refrigerate any remaining wedges.