Marylou's Chicken El Toro

INGREDIENTS

• 4 skinless, boneless chicken breast halves
• 1 tablespoon vegetable oil
• 1 small onion, diced
• 1 (16 ounce) jar mild picante sauce
• 1 cup shredded Monterey Jack cheese
• 8 (8 inch) flour tortillas
• 1/2 cup sliced black olives (optional)
• 1/2 cup sour cream (optional)