Fit piecrust into a 9-inch pieplate according to package directions. Fold edges under, and crimp. Prick bottom and sides of piecrust with a fork.
Line piecrust with parchment paper or aluminum foil; fill with pie weights or dried beans.
Bake at 400° for 10 minutes. Remove weights and parchment paper; bake 5 more minutes, and set aside. Reduce oven temperature to 350°.
Melt butter in a skillet over medium heat; add onion, and cook 3 to 4 minutes or until tender. Add garlic; cook 1 minute. Remove from heat; stir in spinach soufflé.
Whisk together eggs and half-and-half in a medium-size bowl. Stir in spinach mixture, cheese, and next 3 ingredients. Pour mixture into prepared piecrust.
Bake at 350° for 40 to 45 minutes or until a wooden pick inserted in center comes out clean. Let stand 10 minutes before serving.
Note: For testing purposes only, we used Stouffer's Spinach Soufflé, found in the frozen food section of the supermarket.