Place the drained and rinsed black beans in a large mixing bowl. Mash using a potato masher or the back of a large wooden spoon until all the beans have been mashed. The consistency should not be a black bean puree, just mashed beans. Add the cumin, chili powder and mustard powder. Add in a sprinkle of salt to taste, if desired. Set aside.
In a non-stick frying pan, add in 1 1/2 tsp (1/2 Tbsp) canola oil over medium heat. Add in the onion, and the green and red bell peppers. Cook until the onions are translucent. Using a garlic press, squeeze in the garlic cloves and stir until fragrant, about a minute. Remove from the stovetop.
Add the cooked vegetables to the mashed beans, and the egg and dried bread crumbs. Stir all the ingredients together.
Divide the bean mixture into 12 equal portions, and form into cakes. Press each cake gently into the cornmeal to lightly coat both sides.
Heat a large non-stick frying pan over medium-high heat. Add in the remaining 2 Tbsp canola oil. Place the bean cakes in the pan and cook for about 10 minutes, turning once, to cook through and brown both sides. Serve immediately.