Heat a large Dutch oven or heavy bottomed pot over medium-high heat. Add the olive oil and butter, swirl to coat the bottom of the pot. Add the steak, seasoning well with salt and pepper. Cook until steak is browned on all sides, approximately 2-3 minutes.
Add the onions and mix well to combine. Cook the onion until just starting to soften, approximately 3-4 minutes. Add the garlic and bell pepper. Stir to combine and continue to cook over medium heat for an additional 3-4 minutes.
Over medium heat stir in the tomato paste, Italian seasoning, chili powder, and cumin. Cook, stirring constantly, for 1 minute. Increase heat to medium-high and add the pasta sauce, chopped tomatoes, and beef stock. Stir well to combine. Bring to a simmer, cover, and reduce heat to low. Simmer, covered, for approximately 20-30 minutes.
Remove the lid and add the BBQ sauce, black beans, and cannellini beans. Mix well to combine. Simmer for an additional 5-10 minutes before seasoning with additional salt, pepper, or BBQ sauce, to taste. Serve with your favorite garnishes including Doritos Nachos Cheese, shredded mozzarella, chopped cilantro, and green onion. Enjoy!