1. Place a large, deep-sided skillet over med-high heat, add 1 TBSP oil, and the beef. Season the beef with salt and pepper, place it in an even layer in the pan, and cook until nice and brown. (tip: I spread the beef out in the pan and then let it brown almost entirely on one side. This gets things nice and crispy.) Transfer the browned beef to a plate/tray for now. Drain the pan.
   
2. Put the pan back on the stove over medium heat now and add 1 TBSP oil. When it’s hot, add the onion, bell pepper, celery, and carrot. Season lightly with salt and pepper. Cook for 3 minutes, stirring occasionally. Add the cinnamon, chili powder, garlic, and tomato paste. Cook, stirring frequently, for about 1 minute (this toasts the spices, caramelizes the tomato paste, and knocks the rawness off the garlic). Add the ketchup and Worcestershire sauce. Stir to combine. Add the beef back into the pan, along with the stock. Taste and adjust for seasoning (more ketchup, salt, etc.)
   
3. Once everything is heated through, it’s ready to serve, but it tastes better the longer it sits. So, I like to simmer the mixture over low heat, partially covered to catch splatters, for about 15 minutes before serving in bowls and topping with avocado, sour cream, and the cheesy croutons.

    

For the Cheesy Croutons:

In a large skillet over med-low heat, add about 3 to 4 tablespoons of olive oil along with the bun pieces and cheeses. Toast them, stirring all the while, until golden and very brownd – about 5 to 6 minutes, depending on the size of your pan, etc.