Chicken with Walnuts and Spinach

1/3 cup chopped onion
1 Tbsp olive oil
1 cup walnut pieces, chopped
1 cup baby spinach, chopped
1/2 cup grated provolone
4 thin-sliced, boneless, skinless chicken breasts, seasoned with 1/4 tsp salt and 1/4 tsp black pepper

1. Heat oven to 375. In frying pan, cook onion in oil over medium-low heat until softened, 5 minutes. Add 1/2 cup walnuts and cook 1 minute. Increase heat to medium. Add spinach. Cook until wilted, 2 minutes.
2. Put mixture in bowl and stir in cheese. Divide among chicken slices and roll up to enclose. Brush or spray chicken with remaining oil and roll in remaining nuts. Bake on greased baking sheet 30 to 35 minutes.

Source: Prevention Magazine, February 2011