Preheat oven to 400 degrees. Halve, peel, and thinly slice 1⁄4 the red onion. Place in a medium bowl with 1 tablespoon white wine vinegar and set aside to pickle. Mince or grate the garlic. Peel the carrot. Using your peeler, shave the carrot and celery into ribbons, rotating the carrot as necessary. Place the celery and carrot ribbons in a medium bowl of ice water and set aside.

Cook the chicken: season the chicken with the blackening seasoning, coating it on all sides. Heat 1⁄2 tablespoon olive oil in a medium pan over medium-high heat. Add the chicken and cook 3-4 minutes per side, until the exterior becomes slightly charred. Transfer chicken to a baking sheet and bake until cooked through, another 6-8 minutes.

Add the pancetta to the same pan and cook over medium heat for 3-4 minutes, until golden brown and crispy. Set the pancetta aside, keeping the drippings in the pan.

Make the tomato-horseradish vinaigrette: reduce the heat to low and whisk 2 tablespoons tomato paste and the minced garlic into the pancetta drippings. Cook for 1 minute, stirring, then remove from heat and whisk in 1 teaspoon horseradish, remaining white wine vinegar, 2 tablespoons olive oil, and hot sauce to taste. Season with salt and pepper.

Tear the Romaine lettuce leaves into bite-sized pieces. Drain and dry the celery and carrot ribbons. Roughly chop the olives. Thinly slice the chicken against the grain.

Toss lettuce, celery, carrot, pickled red onion, and olives together and mound on a plate. Top with the pancetta and sliced chicken, then drizzle with the tomato-horseradish vinaigrette. Enjoy!