Make the filling. Place the scooped-out zucchini flesh into a mesh strainer and gently press out any excess water. You should be left with 1 cup flesh. Chop any coarse pieces and transfer to a medium bowl with the egg, bread crumbs, cheese, garlic, tomatoes, lemon zest, thyme, pine nuts, and ¼ teaspoon salt. Mix until combined, using your hands if necessary.