The night before: Mix the yeast into the water in the measuring cup. Let sit.
In the bowl of your stand mixer, mix together the flour, garlic salt, oregano, pepper, and salt. Make a well in the center and poor in the yeast mixture. With the hook attachment, mix until combined. Knead until the dough forms a shaggy ball, about 5 minutes. Turn the dough out onto a lightly floured surface and form into a ball. Place in a well oiled bowl and flip. Cover and let rest until doubled in size. After rising, wrap in oiled plastic wrap and store over night in the fridge.
When ready to make the pizza:
Preheat the oven to 500 degrees F. Let it preheat for at least 30 minutes. If using a pizza stone, make sure it is in the oven preheating as well.
Meanwhile, grill the onion, over medium heat (if desired). Slice into smaller bites and set aside.
On a clean lightly floured surface, divide the dough in half. Roll out each half into a 10″ round (check out thekitchn’s tip on rolling out the dough onto parchment paper). Spoon barbecue sauce over the surface leaving a thin border. Top with pulled pork, cheese, and red onion. Bake for 10-12 minutes checking the dough for crispness.
Meanwhile, whisk the sour cream and guac together to form a smooth paste. Spoon into a ziplock bag and snip off the edge; set aside.
Remove from oven and let rest for a few minutes. Top with the avocado spread using the ziplock bag and squeezing onto the pizza in a zigzag.