Crockpot Tostada

3/4 pound ground turkey
1 eggplant, cubed
1 cup fresh or canned salsa
1 (6−oz) can tomato paste
1/4 cup chopped fresh parsley
1 tablespoon chili powder
1 teaspoon ground cumin
1 teaspoon dried oregano
1 (10−oz) pkg. frozen corn, thawed
1/2 cup plain lowfat yogurt
2 cups shredded lettuce
1/2 cup sliced ripe olives
1/2 cup low fat shredded cheese
4 pita rounds, halved, toasted