Heat olive oil in a large skillet or Dutch oven over medium-high heat. Add the Italian sausages and brown them on all sides, about 8-10 minutes. Remove sausages and set aside.

In the same pan, add sliced onions and cook for 5-6 minutes until they start to soften and caramelize, stirring occasionally.

Add the sliced bell peppers to the pan and cook for another 5-7 minutes until they begin to soften but still have some texture.

Stir in the minced garlic and cook for 1 minute until fragrant, being careful not to burn it.

Pour in the red wine (if using) and let it simmer for 2 minutes to reduce slightly and cook off the alcohol.

Add the crushed tomatoes, oregano, basil, red pepper flakes (if using), salt, and black pepper. Stir everything together to combine.

Return the browned sausages to the pan, nestling them into the sauce and vegetables.

Reduce heat to medium-low, cover, and simmer for 25-30 minutes, turning the sausages occasionally, until they're cooked through and the flavors have melded together.

Taste and adjust seasonings as needed. The sauce should be rich, slightly sweet from the peppers, and well-balanced.

Garnish with fresh parsley and basil before serving hot.