On a baking sheet, arrange the baguette slices and brush one side with 2 tbsp. oil; season. Bake at 350° until golden, 15 to 20 minutes. Rub with the garlic. Using a vegetable peeler, shave the asparagus into long ribbons and cut off the tips. In a medium bowl, whisk the lemon zest and juice and the remaining 1 tbsp. oil. Toss with the shaved asparagus and tips; season. Top the toasts with the Brie; bake just until the cheese softens, 1 to 2 minutes. Top the toasts with the asparagus; season with pepper.