Start by roughly chopping the spinach into 1/2-inch pieces and shredding the pepper jack cheese if not already shredded. In a small bowl, combine the spinach, pepper jack cheese, salt, and black pepper, mixing until evenly distributed. Set the filling aside. This prep work ensures you're ready to assemble without delays once the chicken is pounded.

Place each chicken breast between two pieces of plastic wrap or parchment paper. Using a meat mallet or rolling pin, pound the chicken to an even 1/4-inch thickness, working from the center outward with gentle, controlled strikes. This ensures even cooking throughout and creates enough surface area for a good filling-to-chicken ratio. Pat the chicken dry with paper towels before proceeding to remove excess moisture.

Lay out each pounded chicken breast on a clean work surface. Divide the spinach-cheese filling from Step 1 evenly among the chicken breasts, spreading it across the surface while leaving a 1/2-inch border on all sides. Starting from one short end, roll each breast tightly, tucking in the sides as you go to contain the filling. Secure each roll with 2-3 toothpicks along the seam to prevent unrolling during cooking. I find that using wooden toothpicks (soaked in water for 10 minutes beforehand) prevents them from scorching in the oven.

In a shallow bowl, combine the Panko bread crumbs, Cajun seasoning, garlic powder, and red pepper flakes, stirring until the seasoning is evenly distributed throughout the crumbs. Brush or lightly coat each chicken roll with olive oil on all sides, then roll in the seasoned breadcrumb mixture, pressing gently so the coating adheres. The oil helps the breadcrumbs stick and creates a golden, crispy exterior when baked.

Preheat your oven to 350°F. Place the breaded chicken rolls seam-side down on a lightly greased baking sheet, spacing them about 2 inches apart to allow for even heat circulation. Bake for 35-40 minutes, until the coating is golden brown and the internal temperature reaches 165°F when measured with an instant-read thermometer inserted into the thickest part of the chicken (away from the filling). The spinach will wilt and the cheese will melt completely during baking, creating a creamy, flavorful interior.

Remove the baking sheet from the oven and let the chicken rest for 5 minutes on the sheet—this allows the residual heat to finish cooking the interior and lets the cheese set slightly so it doesn't ooze out immediately when cut. Carefully remove the toothpicks and transfer to a serving platter. Let it cool for another minute or two before serving to avoid burns from hot filling.