How to make it
Make the slaw: combine cabbage, cilantro and lime juice in a small bowl. Toss until well combined and season with salt and pepper. Set aside.
Heat the oil in a large skillet over medium-high heat. Add the onion and cook until softened, about 5 minutes. Add the garlic and cook, stirring, 1 minute.
Add the beef and salt and pepper and cook, breaking up the meat, until browned, about 3 minutes. Add the tomato paste, chili powder, and oyster sauce and cook, stirring, about 2 more minutes.
Meanwhile, heat the refried beans in a small saucepan. Thin the sour cream with about 2 Tbsp. water in a small bowl.
Spread the beans on the tostadas, then top with the beef and cheese. Drizzle with the sour cream. Top with slaw and more cilantro.