Brown the sausage in a large skillet or Dutch oven over medium-high heat, breaking it into small pieces with your spoon as it cooks. This should take about 5 minutes. Don't rush this step—those browned bits are pure flavor gold.
Add the onion and bell pepper to the skillet with the sausage. Cook for about 3-4 minutes until they start to soften. The vegetables will pick up all that glorious sausage flavor.
Toss in the garlic and cook for another 30 seconds until fragrant. Your kitchen should smell absolutely amazing by now.
Add the rice to the skillet and stir for about 1 minute, coating it with the fat from the sausage. This step is crucial for flavor development, so don't skip it!
Pour in the chicken broth and diced tomatoes (with their juice). Add the Italian seasoning and red pepper flakes if using. Season with salt and pepper to taste.
Bring everything to a boil, then reduce heat to low, cover, and simmer for about 15-18 minutes, or until the rice is tender and has absorbed most of the liquid.
Stir in the frozen peas and continue cooking for about 2 minutes until they're heated through. The residual heat will cook them perfectly without turning them mushy.
Remove from heat and stir in the Parmesan cheese until melted and incorporated.
Let the dish rest, covered, for 5 minutes. This allows the flavors to meld and any remaining liquid to be absorbed.
Fluff with a fork, garnish with fresh herbs, and serve with additional Parmesan cheese if desired.