Heat oven to 375°F. Lightly spray cookie sheet with cooking spray. Mix onions, cheeses and mayonnaise until well blended and soft.
Unroll dough on work surface, but do not separate. Firmly press perforations to seal. Spread cheese mixture evenly over dough. Starting with 1 short side, roll up rectangle; pinch edges to seal. Cut roll into 16 slices (about 3/4 inches wide). Place cut side down on cookie sheet. Sprinkle with chives.
Bake 12 to 15 minutes or until golden brown. Immediately remove from cookie sheet; cool 3 minutes. Serve warm.