Preheat oven to 400 degrees F. (375 degrees F if using convection oven) .Butter and flour bottom and sides of a 9-inch tart pan with a removable bottom. Unroll pie crust and press into tart pan. Pressing lightly on bottom and up sides. With fork, prick bottom a few times. Brush on egg white. Put pan on a baking sheet and bake 10 minutes. Let cool completely.
In medium skillet, heat oil over medium-high heat. Add pancetta; cook 5-7 minutes until browned. Drain on paper towel. Set aside. In medium bowl, beat eggs. Whisk in mascarpone, gruyere, green onion, spinach, tomatoes, pancetta, salt and pepper. Pour into cooled pie crust; bake 15-18 minutes until mixture is set and top is golden.
Cool tart 10 minutes, remove bottom of pan to release tart. Cut into wedges. Serve with fresh fruit.