For the tortilla bowls: Preheat the oven to 400 degrees F.
Brush the tortilla bowls inside and out with the butter and place on a parchment-lined baking sheet. Bake until just golden and firm, about 5 minutes. Set aside.
For the pork: Cut the pork into 3 pieces. Rub with the taco seasoning.
Heat a large cast-iron skillet over medium-high heat and add the oil. When hot, add the pork and brown on all sides, about 3 minutes. Add the onion and some salt and pepper and cook, tossing, until the onion begins to wilt, about 2 minutes. Transfer to the top rack of the oven and roast until the pork is cooked through and measures 145 degrees F on an instant-read thermometer, 15 to 20 minutes. Let the pork rest 5 minutes, then thinly slice. Return the pork the skillet and toss to combine with the onions.
For the vegetables and beans: Meanwhile, toss the bell peppers, jalapeno, onion and zucchini on a baking sheet with the oil and taco seasoning. Season with salt and pepper. Roast on the top rack of the oven at the same time as the pork, tossing occasionally, until the vegetables are browned and tender, 20 to 25 minutes. Mix the beans into the vegetables on the baking sheet.
For the sweet and spicy BBQ sauce: While the pork and vegetables roast, make the sauces. Stir together the ketchup, cider vinegar, brown sugar, taco seasoning and chipotle and adobo sauce in a medium bowl.
For the white BBQ sauce: Stir together the mayonnaise, sour cream, cider vinegar, horseradish, granulated sugar and garlic in a separate medium bowl. Season with hot sauce and salt.
For topping and serving: Fill 6 of the tortilla bowls with the vegetable and beans and 6 with the pork and onions. Drizzle the sweet and spicy BBQ sauce over 3 of each filling and sprinkle with the Cheddar. Drizzle the white BBQ sauce over the remaining 3 of each filling and sprinkle with the pepper jack. Bake until the cheese is melted and the sauce is bubbly, 5 to 7 minutes. Top with sour cream and sliced scallions.