For the cauliflower: In a large skillet, heat the olive oil over medium-high heat. Add the cauliflower and cook until it begins to soften, 3 to 4 minutes. Add the chili powder, garlic salt and oregano. Cook another 2 minutes, stirring frequently. Stir in the salsa and 1/4 cup water. Bring to a simmer and reduce the heat to low. Cook until the liquid has been mostly absorbed by the cauliflower, about 5 minutes.
For the black beans: In a small skillet, heat the olive oil over medium heat. Add the onions and saute until tender and translucent, 6 to 7 minutes. Add the black beans with their liquid and the sriracha. Bring to a simmer and reduce the heat to low. Simmer on low for about 10 minutes. Use a wooden spoon to gently mash the beans, leaving some texture.
For the tacos: Build the tacos with the tortillas, black beans, cauliflower and desired toppings.