- Heat the olive oil in a large, shallow saucepan over medium heat. Add the onion and cook until slightly translucent. Add the bell pepper and garlic and cook for a couple of minutes more, until the garlic is fragrant.
- Add the tempeh, broth, crushed tomatoes, tomato paste, liquid aminos, maple syrup, cumin, parsley, thyme, and paprika. Cook, stirring occasionally, until the tempeh is tender and the sauce is thick, 10 to 12 minutes.
- Add the salt and pepper, then remove from the heat. Serve on the burger buns, slathered with mayonnaise and topped with avocado (if using).