In a large skillet, heat the olive oil over medium heat. Add the chicken pieces and season with salt, black pepper, and red pepper flakes. Cook for about 5-7 minutes, stirring occasionally, until the chicken is browned and cooked through.
Add the minced garlic to the skillet and cook for an additional 1-2 minutes until fragrant.
Stir in the broccoli florets and cook for about 3-4 minutes, until they are bright green and tender-crisp.
Add the fresh spinach to the skillet and cook for another 2-3 minutes, stirring until the spinach is wilted.
Remove the skillet from heat and drizzle with lemon juice. If desired, sprinkle with grated Parmesan cheese before serving.