Strawberry Rhubarb Crumble Gelson's

Ingredients

• ¾ stick unsalted butter, chilled, cut into ½” cubes, plus more for greasing pan
• ⅔ cup plus ½ cup granulated sugar, divided
• ½ vanilla bean, split lengthwise
• 1 lb strawberries, hulled and halved
• 12 oz rhubarb, ends trimmed, cut into ½” pieces
• ¾ cup all-purpose flour
• Kosher salt, to taste
• ½ cup old-fashioned oats
• ½ cup hazelnuts, lightly toasted, husked, and coarsely chopped