Make the potatoes: Place the potatoes on the baking sheet and toss with the olive oil until thoroughly coated. Spread the potatoes into an even layer. Season with a couple of pinches of salt and pepper.
Make the roasted garlic: Slice the top off the garlic bulb so all the individual garlic cloves are trimmed. Place garlic bulb on a square of aluminum foil (about 8 inches/20 cm square) and drizzle the top of the cloves with the olive oil. Wrap the garlic bulb entirely in the foil and place it on the baking sheet with the potatoes.
Make the pesto: In a food processor, combine the pesto ingredients and process until mostly smooth, stopping to scrape down the bowl as necessary. Keep the pesto in the processor because we will add the roasted garlic as the final step.
Assemble the salad: this is the important part where you need to act fast; I like to assemble the salad very quickly so that it’s warm when I serve it. Grab a large serving bowl and place the arugula in the bottom of the bowl. You can break it up into smaller pieces with your hands a bit. Then, remove the potatoes from the oven and quickly place them into the serving bowl on top of the arugula.
If you want to make this recipe easier, I would advise just mincing the garlic and tossing it with the potatoes before roasting in the oven.
For the pesto, I'm a fan of reducing the olive oil in this recipe by a tablespoon or two and replacing it with water. You shouldn't notice a big difference.