Season roast with salt and pepper, coating evenly on all areas.
Place seasoned roast in slow cooker. Add beef broth around the roast; cover and slow cook on low for eight hours.
Shred the roast with two forks and set aside.
Heat corn tortillas on a large skillet over medium low heat for 7-10 minutes or until tortillas become firm and curl up a bit. Do not char.
Make pico de gallo: Combine tomato, onion, jalapeño, cilantro, lemon juice and salt in a small bowl. Stir!
Spread two to three tablespoons of mashed avocado on each tostada. Top with shredded beef, romaine, pico de gallo and cheese. Repeat with remaining ingredients.