In a large ziploc bag, toss together the sweet potato cubes, pepper slices, onion slices, olive oil, lime juice, brown sugar, chili powder, garlic powder, oregano, smoked paprika, cumin, salt, and black pepper. Let sit in the refrigerator for at least 30 minutes or overnight to marinate.
When ready to cook, heat oven to 400F. Spread the veggies on a parchment-lined baking sheet and roast for 30-40 minutes, or until sweet potato cubes are fork-tender.
Meanwhile, while the veggies cook, make the chipotle crema. To make this, whisk together the sour cream, half and half, adobo sauce, and salt. Store in the refrigerator until ready to use.
To serve, top the butter lettuce leaves with equal amounts of roasted veggie filling. Drizzle with the chipotle crema and sprinkle with the queso crumbles. Serve warm.