1. Heat broiler. Lightly toast pita halves under broiler, about 1 minute.
2. Finely grind pistachios in food processor. Add goat cheese and lemon juice. Whirl just until combined.
3. Cut tomatoes into quarters or thin slices. Spread each pita half with 1/2 teaspoon pistachio mixture. Top with tomato wedge or slice, a sprinkling of rosemary and a grinding of black pepper. Place on baking sheet.
4. Broil pitas on baking sheet until warmed through, about 2 minutes. Serve immediately.