Mix the lime juice with the olive oil, 1/2 teaspoon salt, 1/4 teaspoon ground pepper and rosemary in a bowl. Pour on top of the chicken, in a container. Cover and refrigerate anywhere from 1/2 hour up to 12 hours.
Heat a medium-sized sauté or grill pan over medium-high heat. Add corn or safflower oil; once it is hot but not smoking, add the chicken. Sauté until golden brown and cooked through, about 5 minutes per side. Remove from the pan, place on chopping board to cool. When cool enough to handle, slice into diagonal strips about a 1/2-inch wide.
To make the guacamole:
Place the jalapeño and garlic cloves in a small baking dish under the broiler, for 6 to 9 minutes, until completely cooked through, soft and skin is charred. Once cool enough to handle, peel garlic and mince along with chiles.
Place diced avocado in a mixing bowl. Add the charred and minced garlic and jalapeños, gently tossing everything together well. Incorporate the corn and tomatoes. Squeeze the lime juice on top and sprinkle the salt. Mix it all together.
To assemble tacos:
In an already hot skillet or comal set over medium-low heat, heat the tortillas. It will take about 1 minute per side.
Place the tortillas in a tortilla warmer or wrap them in a clean kitchen towel or cloth napkin. Serve them together with the guacamole and the chicken at the table and assemble your tacos!