Heat oven to 450F.
Place potatoes, onions and crushed garlic in a bowl and toss with just enough EVOO to coat, a couple of tablespoons. Season liberally with salt and pepper, place on baking sheet and place in oven. Roast 45 minutes, turning once.
Place green beans or asparagus in bowl with tomatoes and pitted olives, dress with a little EVOO, salt, pepper and place on baking sheet. Roast 30 minutes.
Meanwhile, heat a cast-iron skillet or griddle or grill pan over medium-high heat. Coat chicken lightly in EVOO and season with salt and pepper. Cook chicken 12 minutes, turning once, then thinly slice on an angle.
While chicken cooks, place shallot, herbs and mustard in food processor and season with salt and pepper. Pulse chop to finely chop the mixture then stream in about 1/4 to 1/3 cup EVOO to form a pesto-like sauce. Scrape sauce into a large, shallow bowl.
Pile roasted vegetables, potatoes, onion, tomatoes, olives and arugula into a bowl. Top salad with sliced chicken and serve with crusty baguette.