Preheat the oven to 375F (190C) and lightly grease a 9x9 inch baking dish, or something similar in size.

Slice the pears into pieces about 1/4 inch thick, peels on, and toss them in a large bowl with the brown sugar, cornstarch, lemon juice, vanilla, cinnamon, and salt until every slice is coated. Pile the mixture into the prepared dish and spread it level.

Make the topping: whisk the flour, oats, brown sugar, cinnamon, ginger, and salt together in a bowl, then add the cold cubes of vegan butter. Rub the butter into the dry mix with your fingertips or a fork until you get clumps the size of small peas that hold together when squeezed.

Slide the bowl of topping into the freezer for 15 minutes while the oven finishes heating. Cold vegan butter melts later in the bake, and that is what keeps the crumble crisp.

Scatter the chilled topping evenly over the pears in loose clumps, and do not press it down. A loose layer bakes into crunchy ridges, while a packed one turns into a dense roof.

Bake for 35 to 40 minutes, until the filling bubbles at the edges and the top is golden brown. If the topping darkens before the filling is bubbling, lay a piece of foil loosely over the dish and keep baking.

Let the crumble rest for 15 minutes before serving. The cornstarch needs that time to set, so the filling cuts into neat jammy spoonfuls instead of running across the plate.