In cast iron pan over medium heat, add butter, onions and brown sugar. Cover and continue cooking on medium-low heat until caramelized and deep brown in colour, approximately 30 minutes. Add garlic, cumin and chili powder and cook 2-3 minutes longer until fragrant. Remove from heat and place onion mixture in a dish.
In same (now empty) cast iron pan, add 2 tablespoons olive oil. When shimmering, add cubed sweet potato and cook on medium-high heat, stirring constantly until tender. Season with salt & pepper. You're looking to brown the sweet potato, approximately 5 minutes. Remember, brown = flavour.
Turn heat to medium low and add onion and spice mixture back to the pan, stirring to combine. Add the can of drained black beans and cook until warmed through and flavours combine, approximately 5 minutes. Season generously with salt & pepper: don't be afraid to season!
Serve immediately, preferably with a poached egg on top and a slice of good 'ol Canadiana on the side: back bacon.