Preheat the oven to 375 degrees. In a large bowl, combine the ground beef, breadcrumbs, egg, onion, jalapeno, chili powder, cumin, salt, and black pepper. Mix until evenly blended.
Press the mixture into a loaf pan and bake for 45 minutes until the internal temperature reaches 160 degrees. Remove from the oven and let the meatloaf cool completely before storing for make-ahead use.
When ready to serve, crumble the chilled meatloaf into a skillet over medium heat. Warm the crumbles for 5 to 7 minutes, stirring occasionally, until heated through and slightly crisp at the edges.
While the meat warms, mash the avocados in a medium bowl. Stir in the shredded cabbage, lime juice, and cilantro until the slaw is evenly coated.
Spoon the warmed meatloaf into the tortillas and top each taco with a generous scoop of avocado slaw. Serve right away.