Coat large skillet with cooking spray; heat over medium-high heat until hot. Add chicken, mushrooms and onion; cook and stir 2 to 4 minutes or until chicken is no longer pink and vegetables are tender.
Reduce heat to medium. Add rice, ricotta cheese, spinach, olives, nuts, garlic, oregano and lemon pepper; cook and stir 3 to 4 minutes until well blended and throughly heated.
Working with 1 phyllo sheet at a time, spray with cooking spray; fold sheet in half lengthwise. Place 3/4 to 1 cup rice mixture on one end of phyllo strip. Fold left bottom corner over mixture; forming a triangle.
Continue folding back and forth into triangle to end of strip. Repeat with remaining phyllo and rice mixture. Place triangles, seam side down, on baking sheet coated with cooking spray. Coat top of each triangle with cooking spray. Bake at 400° F 15 to 20 minutes or until golden brown.
NOTES : to toast nuts, place on baking sheet and bake at 350° F 5 to 7 minutes or until lightly browned.Servings: 4 to 6