Add a bit of oil to a frying pan over medium high heat. Cook 1 cup chopped onion until it turns translucent, about 1-2 minutes.
Add 1 lb ground beef. Break apart with a flat wood spatula and mix in with the onion. Cook until beef turns brown and is no longer pink.
Sprinkle 1 Tbsp all purpose flour overtop and mix together.
Add 1 cup black beans, 1 grated carrot, 14 oz pizza sauce, ¼ cup parmesan cheese, 1 tsp italian seasoning, 1 tsp garlic powder, and ½ tsp dried oregano. Mix together and cook until it thickens, 1-2 minutes.
Preheat the broiler. Spread butter over both sides of 4 hamburger buns (there will be 8 pieces total). Broil the buns on the middle rack for 1-3 minutes on a baking sheet lined with parchment paper. Until it reaches your desired crispiness (we like ours crispy!).
Remove buns from the oven. Spoon the ground beef mixture on top of each bun. Divide the 1 ½ cups shredded mozzarella evenly over top of each one.
Place back in the oven to broil on the middle rack for another 2-3 minutes, until cheese is melted and bubbling. Remove and serve immediately.
Recipe Notes:
This recipe is easy to adapt. Any ground meat will work. You can use spaghetti sauce or pizza sauce: cheddar cheese or marble cheese instead of mozzarella. Black beans can be replaced with kidney beans, chickpeas or lentils. Basically, you can use this recipe as a guide but create your own unique variation.
I prefer to cook on the middle rack when using my broiler. The top rack burns too easily in my oven.
Watch the recipe carefully when using a broiler. Things can burn quickly, so it's best to keep an eye on them. You only need a minute or two for toasting the hamburger buns. And another minute or two to melt the cheese.
The ground beef mixture makes delicious leftovers! Just store it separately from the hamburger buns so that the bread doesn't get soggy.
You can spread mayonnaise or butter on the toasted buns before adding the ground beef mixture. You can also add hot sauce or ketchup for extra flavor.