In a large bowl, combine minced garlic, lime juice, olive oil, cumin, chili powder, salt, and black pepper to create a marinade.
Add the flank steak to the marinade, ensuring it's well-coated. Cover and refrigerate for at least 1 hour (or up to overnight for deeper flavor).
Preheat your grill or grill pan over medium-high heat.
Remove the steak from the marinade and place it on the hot grill. Cook for about 6-8 minutes on each side, or until desired doneness (medium-rare is recommended).
Once cooked, let the steak rest for 10 minutes before slicing it against the grain into thin strips.
While the steak is resting, prepare your tostadas. Spread a generous layer of refried beans on each tostada.
Top each tostada with the sliced carne asada, followed by a spoonful of pico de gallo and slices of avocado.
Sprinkle crumbled queso fresco over the top and garnish with fresh cilantro.