Heat the vegetable oil in a large skillet over medium-high heat. Add the ground beef, half of the minced onion, 1 teaspoon salt and the chipotle chile powder; cook, stirring and breaking up the meat with a wooden spoon, until the meat is browned and the onion is tender, about 7 minutes.
Add the tomatoes, beans and zucchini and cook, stirring occasionally, until the zucchini is just tender, about 6 minutes.
Meanwhile, toss the coleslaw mix, lime juice, and salt and pepper to taste in a bowl.
Divide the tostadas among plates and spoon the beef mixture on top. Top with the cheese, slaw and the remaining minced onion. Serve with lime wedges.
Photograph by Antonis Achilleos
Recipe courtesy Food Network Magazine