Preheat oven to 375°F. Butter 13 x 9 x 2-inch glass baking dish. Mix first 5 ingredients in medium bowl. Add butter and rub in with fingertips until moist clumps form. Combine pear slices and lemon juice in large bowl. Add remaining ingredients and toss to blend. Transfer filling to prepared dish. Sprinkle topping over. Bake crumble until pears are tender and topping is golden brown and crisp, about 45 minutes. Cool at least 20 minutes. Serve warm or at room temperature.