In a large bowl, whisk together the flour, sugars, allspice and salt. Stir in the oats. Using a pastry blender or two knives (or your fingers), work the butter into the flour mixture until large moist clumps form. Cover and refrigerate until ready to use.
MAKE THE CRISP:
Preheat the oven to 450℉. Spread the frozen berries in a single layer on a paper-towel lined baking sheet. Let thaw for 30 minutes at room temperature.
In a large bowl, combine the thawed berries, pears, lemon juice, sugar and flour; toss well. Transfer to a shallow 2-quart baking dish. Sprinkle evenly with the chilled topping.
Bake until the fruit is tender and the topping is golden, about 45 minutes. Let cool for at least 20 minutes before serving. Scoops of vanilla ice cream are wonderful on top of individual servings.