Line a 4 1/2-by-9-inch loaf pan with plastic wrap, leaving a 1-inch overhang on each long side. Toast oats and cashews in a large skillet over medium-high heat, stirring often, until aromatic and just starting to turn golden brown, 5 to 6 minutes. Transfer to a medium bowl.
Add butter, sugar, cinnamon, corn syrup, molasses, and salt in the skillet, and cook over medium heat, stirring, until butter melts and mixture bubbles, 2 to 3 minutes. Pour hot mixture over oats and cashews, and stir to combine.
Transfer mixture to loaf pan. Using a spatula, press mixture into an even layer. Refrigerate until set, about 30 minutes. Remove chilled mixture from pan using plastic, discard plastic, and cut into 1-inch thick bars.