Choose Bosc pears that are ripe but still a little firm for the filling of this oat-almond crisp -- they'll stand up well to baking.
Preheat oven to 400 degrees with rack in center.
Stir together oats, sugar, almonds, flour, and salt. Add butter and mix with hands until small clumps form and dry mixture is coated in butter. Cover with plastic and refrigerate.
Peel, halve, and core pears, then slice into 1/2-inch-thick pieces. Add to a large bowl and toss with lime juice as you work to prevent pears from browning. Toss with sugar, ginger, flour, and salt. Transfer to a 2-quart baking dish. Remove crisp topping from refrigerator and break into small pieces. Scatter evenly over the top. Transfer to oven and bake until bubbly, 50 to 60 minutes (tent top with foil if browning too quickly). Remove from oven and let cool on a wire rack 20 minutes before serving with vanilla ice cream. Crisp is best eaten the day it's made, but can be stored, covered, for up to 3 days in the refrigerator.