Heat a medium skillet over medium heat, then add the oil to warm through. Once the oil is hot, add the onion slices, give them a good stir in the oil, and spread them out evenly in the pan.
Allow the onions to cook, stirring occasionally, for 5 to 10 minutes or until you start noticing some brown streaks coating the bottom of the pan. Lower the heat to medium-low, add a pinch of salt and continue to cook for 20 minutes until the onions develop a deeper golden-brown color, stirring every few minutes to make sure that the onions don’t burn or stick too much to the pan. If the onions are sticking too much, add 1 to 2 tablespoons water to the pan as needed.
Add the garlic and sauté with the onions for 3 to 5 minutes or until they become fragrant and have softened.
Stir in the sun-dried tomatoes and oregano, as well as the fennel seeds and red pepper flakes (if using), and continue to sauté for about 2 minutes.
Add the balsamic glaze, nutritional yeast, butter beans, bouillon cube, and ¾ cup water, then stir well to combine.
Bring the mixture to a simmer and cook for 5 minutes. To thicken the broth, lightly mash a few butter beans with the back of your cooking spoon and stir everything to combine. Cook for an additional 5 minutes until your mixture is at your desired consistency.
Serve a portion of the beans with some toasted bread, a pinch of black pepper, and vegan Parmesan cheese and enjoy.