Hard taco shells are a crunchy classic!
For the salsa, preheat the broiler. On a rimmed baking sheet, arrange the tomatoes, onion, garlic and jalapeño. Lightly spray with cooking spray. Broil until the garlic skin browns (remove after about 6 minutes) and the tomatoes and onions are tender and blackened in spots (leave for 12 to 15 minutes). Peel the garlic into a food processor. Add the tomatoes, onion, jalapeño and cilantro, if using; season with salt. Pulse until coarsely chopped. Preheat the oven to 350°.
Meanwhile, for the filling, in a large skillet, heat the oil, one turn of the pan, over medium-high. Add the beef and chorizo, stirring occasionally and breaking up with a spoon, until browned, about 5 minutes. Add the cumin and season with salt and pepper. Add the onion, garlic and jalapeño; cook, stirring often, until softened, about 5 minutes. Add the lime juice and about 3/4 cup water; cook, stirring often, until thickened, 5 to 10 minutes.
Place the taco shells on a baking sheet. Divide the cheese among the shells. Bake until toasted and the cheese melts, 3 to 4 minutes. Fill the tacos with the beef mixture and top with the salsa and the lettuce and avocado, if using.