1. Prepare rice according to box directions; cool completely (you can do this a day ahead if you like).
2. Preheat oven to 350°F.
3. In medium bowl, combine rice, artichokes, parmesan cheese, and onion; mix well. Stir in yogurt and mix until well blended.
4. Place one sheet of phyllo dough on a damp kitchen towel (keep remaining dough covered). Lightly spray dough with nonstick cooking spray. Fold dough in half by bringing short sides of dough together. Spray lightly with more cooking spray.
5. Cut dough into 4 equal strips about 3-1/4-inch wide. For each appetizer, spoon about 1 tablespoon of rice mixture about 1 inch from end of each strip. Fold 1 corner over filling to make a triangle that encloses filling. Repeat with remaining dough and filling.
6. Place triangles on greased baking sheet and spray triangles with nonstick cooking spray.
7. Bake for 12 to 15 minutes or until golden brown.