In a large saucepan over medium heat, combine the chopped tomatoes with chiles, tomato sauce, cilantro, chipotles, adobo sauce, lime juice, and salt. Bring to a simmer, stirring. Reduce the heat to medium-low and continue to gently cook for 15 minutes, stirring occasionally.
To prepare the meat filling:
Place a large skillet over medium-high heat and add the oil. When the oil is hot, add the onions. Cook and stir until the onions begin to soften, about 3 minutes. Add the garlic and jalapeno, stirring to incorporate. Cook and stir for an additional 2 to 3 minutes, until the onions are well browned and the garlic and jalapenos soften. Add the meat and toss until heated through and well combined, about 2 minutes. Add 3/4 cup of the tomato sauce to the roast beef mixture, tossing to coat.
Remove the sauce from the heat and add the broth. Using an immersion or standard blender, puree the sauce until smooth, it should be thin. Ladle the sauce into 4 bowls for dipping. Be sure the bowls are large enough so the sauce doesn't slop out when the sandwich is dipped.
Spread the smashed avocado on the both side of the roll. Pile the meat filling on the bottom halves of the sandwich buns, close, and cut each sandwich in half. Arrange each sandwich on a plate with the dipping sauce on the side. Dip and eat!
Recipe courtesy of Ingrid Hoffmann, 2008