Heat oven to 400 degrees F (200C) and line a baking tray with foil. Toss the potatoes, brussels sprouts, garlic, and 1 tablespoon olive oil together in a large bowl and season to taste with salt and pepper. Pour them out onto the pan and roast in the oven for about 30 minutes until browned and tender-crisp, stirring once or twice through cooking.

While the veggies are roasting, Toss together the arugula and pecans. When the the potatoes and brussels are finished cooking, remove from oven and cool for at least 5 minutes, then gently toss them into the bowl with the rest of the salad and drizzle with the remaining olive oil. You can either serve immediately while still warm, or allow it to reach room temperature, or even chill if you'd like.