Wash and dry all produce. Preheat the oven to 400 degrees. Halve, peel, and slice the onion into wedges. Core, seed, and thinly slice the bell pepper. Toss the peppers and the onions on a baking sheet with a large drizzle of olive oil and season with salt and pepper. Place in the oven for 20 minutes, tossing halfway through cooking.

Sear the chicken: Season the chicken on all sides with the Southwest spice blend, cumin, and oregano. Heat a drizzle of olive oil in a large pan over high heat. Sear the chicken for 2-3 minutes per side, then transfer to the baking sheet in the oven for 8-10 minutes, until cooked through.

Core and dice the tomato. Pick the cilantro leaves, then finely chop the stems. Zest and halve the lime. Slice the romaine lettuce into 1/2-inch pieces and place in a large bowl.

Halve, pit, and cube the avocado. Place half in a medium bowl with the lime zest, cilantro stems, and the juice of half a lime. Mash together with a fork until completely smooth. Mix in 1 Tablespoon sour cream. Season with salt, pepper, and additional lime juice, if needed.

Heat the broiler to high or the oven to 500 degrees. Cook the chicken and veggies for an additional 2-3 minutes, until they are slightly charred. Toss the charred veggies into the romaine lettuce along with the tomatoes, cilantro leaves, and cubed avocado. Stir the avocado-lime dressing into the salad and toss until evenly coated. Thinly slice the chicken.

Plate and serve: Serve the chopped salad topped with the sliced chicken and enjoy!