Begin by preheating your Traeger Flatrock griddle (one zone) to medium heat.
Assemble your ingredients and make the horseradish guacamole.
In a bowl, combine the avocado, tomato, onion, cilantro, lemon and horseradish and stir to mix.
Season with Garlic Junkie seasoning and adjust to taste.
Cube the Prime Rib into 1/2 inch dice.
Dice the onion into 1/2 inch pieces.
Finely shred the cheddar cheese.
On the griddle, begin by cooking the onions in the butter until golden and turning translucent (about 5 minutes).
Add the cubed Prime Rib and cook, turning frequently, until golden brown and heated through.
Add the cheddar cheese and cover until the cheese begins to melt.
Warm the tortillas on the griddle until golden brown.
Stir the meat/cheese/onion mixture to ensure the cheese melts well.
Transfer the meat to a bowl and the tortillas to a cutting board.
Top each tortilla with a generous scoop of horseradish guacamole.
Pile meat/cheese/onion mixture atop each tortilla.
Drizzle with hot sauce, if desired, and serve your Prime Rib and horseradish guacamole tacos while hot.