In a large skillet, heat the olive oil over medium heat. Add the diced onion and cook until translucent, about 3-4 minutes. Stir in the minced garlic and cook for an additional 1 minute until fragrant.
Add the diced red bell pepper to the skillet and cook for another 3-4 minutes until softened.
Stir in the orzo, diced tomatoes (with their juice), chicken broth, Italian seasoning, red pepper flakes (if using), and a pinch of salt and pepper. Bring the mixture to a boil.
Reduce the heat to low, cover the skillet, and let it simmer for about 10-12 minutes, stirring occasionally, until the orzo is tender and most of the liquid is absorbed.
Once the orzo is cooked, gently fold in the shrimp. Cover the skillet again and cook for an additional 3-5 minutes, or until the shrimp are pink and cooked through.
Remove the skillet from the heat and stir in the grated Parmesan cheese until melted and creamy. Adjust seasoning with salt and pepper if needed.
Garnish with fresh parsley before serving.