Heat olive oil in a large heavy-bottomed pot or Dutch oven over medium-high heat.
Add the beef cubes and brown on all sides, about 5-7 minutes. Remove beef and set aside.
In the same pot, add the chicken thigh pieces and brown until golden, about 4-5 minutes per side. Remove chicken and set aside with the beef.
Add the sliced onion and bell peppers to the pot. Sauté until softened, about 5 minutes.
Add the minced garlic and cook for 1 minute until fragrant.
Pour in the red wine and scrape the bottom of the pot to deglaze, cooking for 2-3 minutes until the wine reduces slightly.
Return the browned beef and chicken to the pot.
Add the crushed tomatoes, beef broth, dried oregano, dried basil, dried thyme, crushed red pepper flakes, salt, and black pepper. Stir to combine.
Bring the mixture to a simmer, then reduce heat to low and cover the pot.
Simmer gently for 1 hour 15 minutes to 1 hour 30 minutes, stirring occasionally, until the beef and chicken are tender and the sauce has thickened.
Taste and adjust seasoning with additional salt and pepper if needed.
Stir in the chopped fresh parsley just before serving.