Remove leaves from cauliflower head, core, and cut into 1" pieces. Using a peeler, shave celery into long, thin ribbons across its length. Place ribbons in a medium bowl of ice water. Halve and juice lemon. Make Buffalo sauce by melting butter in a small pan over medium heat and whisking in hot sauce with 1 tsp. lemon juice. Alternatively, melt butter in a small bowl in microwave. Rinse chicken breasts, pat dry, and season with 1/2 tsp. salt and a pinch of pepper.

Spread cauliflower florets on prepared baking sheet, leaving enough room to add chicken later. Drizzle with 1 tsp. olive oil and season with 1/4 tsp. salt. Toss to coat evenly. Roast 18 minutes and remove from oven. Cauliflower should be almost fully tender, slightly caramelized, and will finish cooking with chicken breasts.

While cauliflower roasts, heat 1 tsp. olive oil in a medium non-stick pan over medium-high heat. Add chicken breasts to hot pan and sear 4-5 minutes per side, or until well-browned. After cauliflower roasts 18 minutes, remove from oven and add chicken breasts. Top chicken with bleu cheese crumbles (to taste) and brush cauliflower with Buffalo sauce (reserve 1 Tbsp. for plating). Return baking sheet to oven and roast 6-8 minutes, or until chicken reaches a minimum internal temperature of 165 degrees. Wipe pan clean.

In pan used to sear chicken, combine honey, 1 Tbsp. water, and walnuts. Stir to combine and place over medium heat. Bring to a simmer and cook 3-4 minutes, or until water has mostly evaporated and walnuts are sticky and coated with honey.

Drain celery in colander and pat dry. Wipe bowl clean and whisk together 1 Tbsp. lemon juice, 2 Tbsp. olive oil, and a pinch of salt and pepper. Toss with celery and arugula.

Place a serving of arugula salad on a plate and top with candied walnuts. Place chicken and cauliflower florets next to salad. Brush cauliflower with reserved Buffalo sauce (to taste) and serve.