1. Place sweet potatoes in a medium lidded pot; cover with cold water by 1 inch. Bring to a boil; reduce heat to medium and simmer, covered, for 10 to 12 minutes, until fork-tender. Drain, return to pot and mash. Stir in butter, milk, maple syrup and 1/2 tsp of the salt.
2. Meanwhile, in a food processor, combine oats, garlic, rosemary, thyme, 1/2 tsp of the salt and the pepper. Pulse several times until ingredients are roughly chopped. Pour into a bowl and add Parmesan. In a second bowl, beat egg with 2 tbsp water. In a third bowl, blend flour and 1/4 tsp of the salt.
3. Pound chicken breasts to 1/2-inch thickness. Coat each breast on both sides with flour. Dip into beaten egg, allowing excess to drip off chicken. Finally, coat with oat mixture and place on a baking sheet.
4. In a large nonstick skillet, heat 1 tbsp of the oil over medium-high heat. Add 2 of the chicken breasts; cook 4 minutes. Flip over and reduce heat to medium; cook 3 minutes. Repeat with remaining 1 tbsp olive oil and 2 chicken breasts.
5. Top chicken with Parmesan and, if desired, drizzle with warm maple syrup. Serve with sweet potatoes, and, if desired, arugula.