Press tuna between paper towels until barely moist. Combine the breadcrumbs, pesto, and water in a small bowl, tossing well. Pat breadcrumb mixture on both sides of tuna.
Heat a large nonstick skillet coated with cooking spray over medium-high heat until hot. Add tuna; cook 2 minutes on each side or until medium-rare or desired degree of doneness. Remove tuna from pan; keep warm. Stir in vinegar and capers, scraping pan to loosen browned bits; cook 1 minute.
Place a large Dutch oven coated with cooking spray over medium-high heat until hot. Add shallots, and sauté 3 minutes or until tender. Add spinach, and sauté 1 minute. Add wine and pepper; partially cover and cook for 2 minutes or until the spinach wilts. Place tuna over spinach; drizzle with caper sauce.