Allow the corn kernels to thaw, or heat them through if you plan to eat the bowls immediately. Rinse and drain the black beans, then add them to a bowl along with the chili powder and stir until the beans are coated.
To build the bowls, place about 1.5 cups mashed potatoes in each bowl, then top with about 1/2 cup corn kernels, 1/3 cup black beans, about 1/4 cup shredded cheddar, 2 Tbsp BBQ sauce, and a sprinkle of sliced green onions and jalapeño.
Serve the bowls immediately, or refrigerate until ready to eat. To reheat, simply microwave until the mashed potatoes are hot and the cheese is melted.