Unfold piecrust, and place on a lightly floured surface. Roll to 1/8-inch thickness. Carefully place piecrust in a 9-inch pieplate; fold edges under, and crimp.
Bake on lowest oven rack at 400° for 8 minutes. Cool.
Sauté chopped green onions in hot oil in a large skillet over medium-high heat 2 minutes. Stir in crabmeat and next 3 ingredients; sauté 2 minutes.
Whisk together half-and-half and next 3 ingredients in a large bowl; stir in cheese and crabmeat mixture. Pour into prepared crust.
Bake on lowest oven rack at 400° for 35 to 40 minutes or until set. Let stand 15 minutes.