Start by heating your cooked barbacoa beef in a skillet over medium heat with a small drizzle of oil. If you're using leftovers, this step brings back that just-cooked texture and flavor. Stir occasionally so it heats evenly without drying out. This should only take a few minutes.
Rinse the tomatoes, jalapeno, and cilantro well before chopping. Dice the tomatoes, onion, and jalapeno into small, even pieces, then finely chop the cilantro. Toss everything into a bowl with salt and fresh lime juice, then mix and taste for balance.
Finely chop the onion and smoosh it with the back of a fork to soften its bite. Combine it with mashed avocado, salt, and lime juice in a bowl. Mix well and taste as you go, adding more salt or lime until it feels right.
Heat each tortilla for about a minute in the same skillet you'll use later for the burritos. Warm tortillas are far more pliable and much less likely to crack or tear when you roll them tightly.
Layer rice, beef, pico de gallo, and guacamole down the center of each tortilla. Don't overfill them, or rolling gets messy. Fold in the sides first, then roll tightly from the bottom up.
Place the rolled burritos seam-side down in a dry skillet over medium heat. Cook for 2-3 minutes per side until golden and slightly crisp. Serve them right away while they're hot and crunchy on the outside.