In a large bowl, combine the ground beef, chopped onion, 1/4 cup crushed corn chips, the egg, chili powder, 3/4 teaspoon salt and 1/4 cup water. Shape into 1-inch balls.
In a large saucepan, heat the olive oil over medium heat. Add the sliced onion and cook until softened, about 3 minutes. Stir in the tomatoes and the remaining 3/4 cup crushed corn chips and bring to a boil. Add the meatballs to the sauce, cover and simmer until the meatballs are cooked through, about 20 minutes. Stir in the beans and cook just until heated through, about 5 minutes.
Preheat the broiler. Using a slotted spoon, spoon the chili meatballs and sauce into the toasted rolls, then top with the cheese. Broil until the cheese is melted, about 2 minutes.