Preheat oven to 400 degrees F. Prepare corn muffin mix according to package directions, adding the egg and substituting buttermilk for the liquid. Pour batter into a greased 9x5x3-inch loaf pan. Bake about 20 minutes or until a wooden toothpick inserted in center comes out clean. Cool 10 minutes. Remove from pan. Cool on a wire rack.
Wash greens; pat dry with paper towels. In a screw-top jar combine olive oil, lemon juice, salt, and pepper. Cover and shake well.
Halve the cornbread crosswise. In a large skillet melt 1 tablespoon of the butter or margarine. Brown one half of the cornbread on both sides in hot butter over medium heat. Remove and repeat with remaining butter and other half of cornbread. Stir together sugar and pumpkin pie spice; sprinkle half of the sugar mixture over each piece of cornbread. Cut each half crosswise to make 6 rectangular pieces (12 total).
To serve, shake dressing and toss with greens. Place a piece of cornbread on each of 12 appetizer plates. Top with greens.