Preheat the Blackstone griddle to medium-high heat.
Place the tomatillos, jalapeños, serranos, and onion directly on the griddle. Char on all sides until blistered and softened, about 6–8 minutes.
Transfer the charred vegetables to a blender. Add the garlic cloves, chicken bouillon, cumin, and just enough water to blend. Blend until smooth and set aside.
Season the flap steak with Blackstone Garlic Pepper seasoning. Cook on the griddle until browned and cooked through, then remove and set aside.
Add a little oil to the griddle and cook the potatoes. Season with garlic powder and a pinch of salt, cover with a dome, and cook until soft and golden, flipping occasionally.
Place a cast iron skillet on the griddle to preheat. Add the cooked steak and potatoes, then pour in the green salsa.
Let everything simmer together until it gently boils and the flavors combine. Adjust salt to taste.
Serve hot with warm tortillas, rice, queso fresco, and a squeeze of lime. Beans can be served on the side if desired.
