Preheat oven to 375 degrees. Place parchment paper on a large baking sheet and set aside.
On a lightly floured surface, unfold the thawed puff pastry sheet. Using a rolling pin, roll sheet out into a 16x12-inch rectangle and carefully place on prepared baking sheet. Bake for 12 to 15 minutes, or until sheet is light pale brown and becomes puffy. Allow pastry time to "deflate" prior to adding cheese and vegetables. Keep oven at 375 degrees for baking the tart.
In a large pot, add about an inch of water and bring to a boil. Add the salt, pepper, and garlic powder. Add asparagus and boil only until crispy-tender, about 5 to 7 minutes.
Sprinkle pastry sheet with shredded fontina cheese leaving about an inch border. Line cooked asparagus over cheese.
In a small bowl, mix together olive oil, minced shallots, and lemon zest. Using a pastry brush, brush olive oil mixture over asparagus. Spritz the tart with a wedge of lemon. Bake for 12 to 15 minutes, or until cheese is melted and puff pastry edges are a beautiful golden brown. Serve immediately.
Notes
Helpful Tip: If you can't find Fontina cheese, you can use provolone, Gruyère, Emmental, or Gouda.