If frozen, thaw shrimp according to package directions. Peel shrimp, and, if desired, devein. Set aside.
Cut bread diagonally into 12 (1/2-inch-thick) slices, discarding ends. Coat both sides with cooking spray, and place on a baking sheet.
Bake at 375° for 5 to 6 minutes or until edges are crisp. Reserve bread on pan.
Peel and coarsely chop avocados, and place in a medium bowl. Add lime juice and next 6 ingredients, and gently combine, being careful to retain small avocado chunks. (Do not mash.) Chill until ready to serve.
Sauté garlic in hot oil in a medium skillet over medium heat 1 minute. Add shrimp, in batches, and cook 2 minutes on each side or just until shrimp turn pink. (Shrimp should be slightly undercooked.) Remove from pan, and place 2 shrimp on top of each baguette slice on baking sheet. Top each with 1 Tbsp. Manchego cheese.
Broil 5 inches from heat 1 to 2 minutes or until cheese melts. Remove from oven, and top each with 1 to 2 Tbsp. avocado mixture. Garnish, if desired. Serve immediately.