Preheat your oven to 400°F and line a baking sheet with parchment paper.
Peel the beets and cut them into 1/2-inch cubes, then toss them on the baking sheet with half of the olive oil, sea salt, and black pepper.
Roast the beets for 25 to 30 minutes until they are tender and slightly caramelized.
While the beets roast, season the chicken breast with a pinch of salt and pepper, then grill or pan-sear over medium-high heat for 6-7 minutes per side until the internal temperature reaches 165°F.
Let the chicken rest for 5 minutes before slicing it into thin strips.
In a large serving bowl, layer the fresh arugula and top with the warm roasted beets and sliced chicken.
Sprinkle the crumbled feta and walnuts evenly over the top of the salad.
Whisk the remaining olive oil with the lemon juice and drizzle it over the salad just before serving.