1. Preheat oven to 425°. Place chicken between 2 sheets of heavy-duty plastic wrap, and flatten to 1/4-inch thickness using flat side of a meat mallet or rolling pin. Sprinkle chicken with pepper and salt.
2. Sauté spinach and 2 minced garlic cloves in 2 tsp. hot oil in a large ovenproof skillet over medium heat 1 minute or until spinach begins to wilt. Transfer spinach mixture to a plate. Wipe skillet clean.
3. Spoon spinach mixture over each breast, leaving a 1/2-inch border around edges. Top with asparagus, and roll up, starting at 1 short side. Tuck in ends of chicken, and secure with wooden picks.
4. Melt 3 Tbsp. butter with 2 Tbsp. olive oil in skillet over medium-high heat; add chicken. Cook 6 to 8 minutes, turning to brown on all sides. Transfer skillet to oven, and bake at 425° for 15 minutes. Transfer to a serving plate, and cover loosely with aluminum foil to keep warm.
5. Melt remaining 2 Tbsp. butter in skillet over medium-high heat; add remaining garlic. Sauté 1 to 2 minutes or until tender and fragrant. Whisk in flour; cook 1 minute. Add white wine; cook, stirring constantly, 1 minute. Whisk in chicken broth and lemon juice; cook 2 minutes or until thickened. Stir in parsley and capers; spoon sauce over chicken. Serve immediately.