1. Cut avocados in half. Scoop pulp into a bowl, and mash with a potato masher or fork until slightly chunky. Stir in 2 Tbsp. red onion and next 5 ingredients. Gently fold in cheese. Place plastic wrap directly on surface of mixture, and let stand at room temperature 30 minutes.
2. Meanwhile, preheat oven to 375°. Finely chop tomatillo.
3. Separate pita rounds lengthwise into two halves. Arrange in a single layer on a baking sheet; drizzle with olive oil.
4. Bake at 375° for 6 to 8 minutes or until toasted. Top each with 1 rounded teaspoonful avocado mixture. Stir together tomatillo, tomato, and remaining 1 Tbsp. red onion. Top avocado mixture with tomatillo mixture. Sprinkle with coarsely ground pepper to taste.
*1 (8.5-oz.) French bread baguette may be substituted for pita rounds. Cut bread diagonally into 42 (1/2-inch-thick) slices, discarding ends.
Note: For testing purposes only, we used Toufayan Bakeries Mini Pitettes.