Heat oven to 450ºF. Pound chicken breasts into thin cutlets. In a small bowl, combine garlic, lemon zest, and Parmesan.
Lay 8 spinach leaves on each chicken cutlet, then sprinkle garlic mixture on top.
Roll chicken up and secure with a toothpick (place toothpick in parallel to seam to make turning roulades easier).
Season chicken with 1/2 tsp each salt and pepper.
Heat 1 Tbsp oil in a large ovenproof skillet on medium-high. Carefully add roulades, seam side down, and cook, turning until browned on all sides, 6 to 7 minutes.
Transfer to oven and bake until cooked through, 8 to 9 minutes more. Drizzle lemon juice on roulades.
While chicken roasts toss together tomatoes, onion, red wine vinegar, remaining 2 Tbsp oil, and 1/2 tsp each salt and pepper. Serve with chicken.