Pat chicken breasts dry with paper towels. Cut into 1-inch cubes and season with salt, pepper, and smoked paprika.
Heat a large skillet over medium-high heat. Add olive oil and 1 tbsp butter.
Sear chicken in a single layer for 3-4 minutes per side until golden and cooked through (165°F). Remove and set aside.
Reduce heat to medium. Add remaining butter to the pan, then add garlic and red pepper flakes. Sauté 30-45 seconds until fragrant.
Pour in chicken broth and scrape up browned bits. Simmer for 2 minutes.
Return chicken to the pan. Add lemon juice, lemon zest, and parsley. Toss to coat and simmer 1-2 minutes.
Serve immediately topped with freshly grated Parmesan cheese.