Preheat the Big Green Egg: Set up your grill for indirect cooking with the ConvEGGtor legs up and the stainless steel grid on top. Stabilize the temperature at 350°F.
Prepare the Brisket: Chop your leftover brisket into half-inch cubes to ensure even coverage and easy eating.
Sauce the Meat: Toss the cubed brisket in a bowl with the red enchilada sauce until well-coated. If the brisket is cold, warm it in a pan with the sauce first until the liquid is mostly absorbed.
Layer the Base: Place a thick layer of tortilla chips in the bottom of a large cast iron pan.
Add Cheese and Beef: Cover the chips with a generous blend of the shredded Monterey Jack and Cheddar, then liberally top with the sauced brisket chunks.
Repeat the Layers: Continue layering chips, cheese, and brisket until the cast iron pan is filled to the top.
Bake on the Big Green Egg: Place the cast iron pan on the cooking grid. Close the dome and bake for 10 to 15 minutes or until the cheese is bubbling and the chips are lightly toasted.
Check for Doneness: Ensure the cheese in the center is fully melted before removing the pan from the grill using heat-resistant gloves.
Add Condiments: Top the hot nachos with dollops of guacamole, sour cream, and salsa. Scatter the pickled jalapeños and fresh cilantro over the top.
Serve Immediately: Place the cast iron pan on a trivet in the center of the table and serve while the cheese is still gooey and the brisket is hot.